You will be presented with the synchronization checklist if you have enabled option Preview changes on Synchronize dialog. In the checklist you can select those synchronization actions you want to actually apply.
In the checklist, there is one row per each synchronization action. For each action, you can see the action type, visualized by icon. Green arrows indicate a new file that does not exist in the target/destination directory and will be copied to the directory that the arrow points to (see note 1). Blue arrows indicate a changed file that will be copied to the directory (overwriting the file with the same name) that the arrow points to (see note 1). And finally red crosses indicate a file that only exists in the target/destination directory and will be deleted (see note 1). For each action you can see also name of the file or directory (directories end with slash and can be distinguished also by an icon), and their attributes in either local or remote directory or both (for updated files). Columns Local/Remote directory indicate location of the files/directories relative to root directory of synchronization.
To select actions to be applied, use checkbox at the very beginning of each row.
To check more actions at a time, select them and use buttons
(Un)Check or context menu. Note that you can select all
actions or certain type (like local file updates) by clicking on respective
section of Status bar (at the bottom of the window).
To add the actions to the existing selection, hold down
Note that initially only those actions that you have requested by your synchronization options will be checked. I.e. if you have not enabled option Delete files, the deletion actions will be unchecked.