is used to "undo" certain actions. Not all actions are supported by Undo. By clicking the drop down arrow, that is next to the Undo toolbar button, you will get a list of items that may be undone. The keyboard shortcut key for this function is <Ctrl> Z. You can find this function in two locations: the toolbar button or under the Edit Menu.
is used to "redo" certain actions. Not all actions are supported by Redo. By clicking the drop down arrow, that is next to the Redo toolbar button, you will get a list of the items that may be redone. The keyboard short-cut key for this function is <Ctrl> Y. You can find this function in two locations: the toolbar button or under the Edit Menu.
When doing multiple functions at a time, it is very useful to use the drop down arrow next to undo/redo instead of just clicking the undo/redo button. This way you can see a whole list of functions performed and undo/redo multiple functions at a time.