In the Actions menu, the Copy to Right, Copy to Left and Copy to Side commands copy the selected files and folders from one side of the view to the other, overwriting any existing files on the target side.
If a folder is selected, only its filtered contents will be copied (same as if the folder was expanded and all visible contents selected). However, if an open folder is selected and any of its children are selected as well, then the folder's selection is ignored and only the selected children will be copied.
By default, a confirmation dialog appears before the copy. To skip the confirmation when the direction of the copy is unambiguous (Copy to Left, Copy to Right), choose Tools | Options 
(Beyond Compare | Settings on macOS), switch to the File Operations page, and clear the Confirm file copy checkbox.
