The Drawer and the Inspector

FS Drawer
FS Inspector
When you click Show/Hide Details in the main window's toolbar for the first time, the main window's drawer will slide to the right to reveal itself.
Alternatively, if you choose Inspector from the Window menu or if you double-click on a pair in the list, the Inspector panel will be opened, and if the drawer is opened, it will slide underneath the main window to hide. The Inspector panel looks pretty much the same than the drawer.
As you can see, the content of the drawer and the inspector panel is exactly the same. The major difference between the two is you can drag the inspector panel pretty much where you want and resize it, while, on the other hand, the drawer will stick to the main window. You can also resize the inspector any way you want it while the drawer, even if you can make it wider, will stick vertically to the main window. So, I guess it's just a matter of preference... Please note that you can select on which side you want the drawer to slide, through the Preferences window. By default, the drawer will slide to the right of the main window, but you can decide to make it slide at the bottom of the main window. See the Preferences window for additional details.

The Controls

Folder Buttons
The 2 buttons on each side of the "double arrows" button, in the middle, are displaying the current elements selected as the source and the destination. You can click on them to select a new item, and you can also drag an item from the Finder directly onto the buttons to set the source and/or the destination of that pair.
Priority Button
The button with the double arrows in the middle is used to select the synchronization priority. It has 3 states: the current one as displayed on the left, pointing to the right to indicate that the source has the priority and pointing to the left to indicate that the destination has the priority. You cycle through the 3 states by simply clicking the button with the pointer, or if you have full keyboard access turned on, just press tab until the button is selected and then press the spacebar to cycle through the 3 states. The synchronization priority will determine the behavior when synchronizing. When both the source and the destination have priority, any file on each side that is not found on the other side will be copied over when synchronizing. If the Delete orphaned files is selected, then the result is quite the opposite: any single file on one side of the pair that isn't found in the opposite side will be deleted or moved to the trash when the synchronization is performed. So, care must be taken before you select the Delete orphaned files! If you're not sure, set the preferences to move orphaned files to the trash instead of deleting them. Or, you could enable the option Keep files recently modified. When this option is enabled, orphaned files that have been modified since the last synchronization will be copied over instead of being deleted. When the synchronization priority is set to the source or the destination, every file that is found on the prioritized side which is not found on the other side will be copied over during the synchronization process. Any file on the non prioritized side that isn't found on the prioritized side will be left there, as long as the Delete orphaned files button is not selected. If it is selected, then any file on the non prioritized side that is not found on the prioritized side will be deleted or moved to the trash. Again, if the Keep files recently modified checkbox is enabled, the files that have been modified on the non-prioritized side since the last synchronization will be left there untouched. Giving the priority to one side and selecting Delete orphaned files will ensure that the prioritized item will be copied over the non prioritized item, resulting in a perfect copy. Even if a file in the non prioritized item is more recent than its matched file in the prioritized item, it won't be copied. Only the most recent files in the prioritized item will be copied. Here is a little table to explain the behaviors:
Table Caption

Synchronization Priority

Orphaned Files

Keep Recently Modified

Missing files on either side

Modified files

Double Priority Button
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Will be copied over to the other side.
Every file that is found to be more recent than its counterpart on the other side will be copied.
Double Priority
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Will be deleted or moved to trash if no file by the same name can be found on the other side.
Every file that is found to be more recent than its counterpart on the other side will be copied.
Double Priority Button
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Will be copied over if they have been modified since the last synchronization. Otherwise, will be deleted or moved to trash.
Every file that is found to be more recent than its counterpart on the other side will be copied.
Left Priority Button
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Every file on the source side that is missing on the destination side will be copied over. Orphaned files on the destination side will be left and not copied nor deleted.
Every file that is more recent on the source side will replace the same file on the destination side. Files that are more recent on the destination side are not copied over the source side.
Left Priority Button
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Every file on the source side that is missing on the destination side will be copied over. Orphaned files in the destination side will be deleted without further notice or moved to trash depending on your preferences.
Every file that is more recent on the source side will replace the same file on the destination side. Files that are more recent on the destination side are not copied over the source side.
Left Priority Button
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Every file on the source side that is missing on the destination side will be copied over. Orphaned files on the destination side will be kept if they have been modified since the last synchronization. Otherwise, they will be deleted or moved to trash.
Every file that is more recent on the source side will replace the same file on the destination side. Files that are more recent on the destination side are not copied over the source side.
Right Priority Button
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Every file on the destination side that is missing on the source side will be copied over. Orphaned files on the source side will be left and not copied nor deleted.
Every file that is more recent on the destination side will replace the same file on the source side. Files that are more recent on the source side are not copied over the destination side.
Right Priority Button
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Every file on the destination side that is missing on the source side will be copied over. Orphaned files in the source side will be deleted without further notice or moved to trash depending on your preferences.
Every file that is more recent on the destination side will replace the same file on the source side. Files that are more recent on the source side are not copied over the destination side.
Right Priority Button
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Every file on the destination side that is missing on the source side will be copied over. Orphaned files on the source side will be kept if they have been modified since the last synchronization. Otherwise, they will be deleted or moved to trash.
Every file that is more recent on the source side will replace the same file on the destination side. Files that are more recent on the source side are not copied over the destination side.
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This popup lets you choose the synchronization mode. There are 3 modes: Automatic, Repeating and Manual. When you choose the Automatic mode, any change that occurs in the folder you synchronize or in one of its subfolder will trigger the synchronization, 30 seconds after the change occurred. NOTE: this will only work with local hard disks that are formatted as HFS+. It will not work with any remote volume even those that are shared by another Mac. This is because this function uses an OS X file system feature that notifies applications when a change occurs in a specific folder or subfolder.

In the Repeating mode, the synchronization is repeated according to the settings you set in the Repeat Sync tab of the main preferences.

In the Manual mode, you select the pairs in the list and click the Synchronize button in the toolbar or select Synchronize from the File menu.
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This text field lets you specify a value in minutes that will be used by File Synchronization to determine whether 2 matched files are different enough to warrant copying the most recent one over the older one. If you're synchronizing with a remote volume and routinely have a slight time difference between your host computer and this remote computer, you can put a value there to compensate for that difference so that files that shouldn't be copied won't.
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This button opens the filter sheet which lets you specify criterias to ignore some files and/or folders.
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This sheet displays the list of criteria that are used to ignore some files and folders. This can speed up the whole synchronization process quite a bit.

The criteria that you can choose are the names, the size, the extension, the file type and the file creator (the file type and creator are a 4 characters code that you can see with a tool such as XRay). Each criteria has its own set of operators that you can use. For example, when selecting the name, you can set the operator to contains, starts with, ends with, is (exactly the value entered) or does not contain. Clicking the + button adds a new criteria, while clicking the - delete the selected criteria. As the dialog warns, be careful in creating those criteria because you have to keep in mind that File Synchronization will have to evaluate each of them with every file contains in the 2 folders that make up a pair, thus increasing the time to do the scan. However, even though the scan can increase, if enough files and folders are ignored or if the files or folders are large, the time to copy the files and folders can be significantly smaller. Double-click to the right of the operator popup to enter the value to be evaluated. Press Enter to validate the input, then click OK when you're done.
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This checkbox lets you decide whether or not the synchronization should generate an error in the event that a pair of files have both been modified since the last synchronization. If you check this box, File Synchronization won't generate a warning and will copy the most recent file over the other, older one.
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This checkbox gives you the ability to include invisible items or not. Usually, it's preferable that invisible items are not included. Invisible items often contain some information about the original folder they reside in which might conflict or result in strange behavior if copied over in another folder.
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These 2 text fields provide the status of the last synchronization. If everything went fine, the status will be The items have been synchronized. If an error did occur at the last synchronization, then the status will read The items have been partially synchronized. If the pair was just added to the list, or if no item have been selected for that pair, or if one item hasn't been selected, the text field will display an appropriate message like No items were selected or The source has not been selected. If one of the item in the pair has been replaced, the status will read The items have not been synchronized. The Last synchronized text field provides the completed date and time of the last synchronization. Again, if the pair is new or if one of the item in the pair has been replaced, then the text field will display Never.