This tool is used to redo (the opposite of undo) a sequence of functions used.
After having undone an operation selecting Edit>Redo will restore the undone operation. If you continue to use Edit>Redo, previous operations you cancelled will be recreated. Listed under the Edit>Redo menu are all the functions that can be redone, by clicking onto one of these, several functions can be reinstated.
If there are no more undone operations to repeat, the Redo tool will appear greyed out on the Edit menu.