You can undo no problem (Control/Command-Shift-Z) but what’s the shortcut for redo? The redo shortcut is normally either Control/Command-Shift-Z or Control/Command-Y. The easy rule of thumb is throw in a shift key. Try it on other shortcuts when you’re trying to do the opposite.
Undo and redo work between saves as long as you haven’t close the program down. You can undo a long way but remember if you go backward and make a small change you will not be able to redo forwards again. That can be annoying.
If you use undo and redo keys often then you may also be a connoisseur of the history panel. Not to be confused with your browser history, the History panel is a common tool in most professional application such as Adobe Suite or AutoDesk. Every time you make a change to you document, that change (panel pane) is logged in the History panel. You can revert your document to a previous state by selecting a pane. This will affectively undo all your changes undo you get to that document state. You can also redo again by selecting a more recent pane and the document will jump to a more recent state.
Most documents will save a limited amount of history steps, typically 20. This value can normally be increased so you can have more undos and redos but the app may run slowly if you have too many. So be mindful you don’t fall off the undo cliff!
The other pit fall of undo redo shortcuts is the broken ladder. Beware the broken ladder. You may have experienced this in Word. You’ve done a few undos, you make a small change, maybe a space or a full stop and snap. You’ve broken the ladder of redo. You can’t get back up with redo the document has now moved along another branch, a branch that has no future.