When working with Photoshop, you may get confused, do something you didn't mean to, or want to get back to your image in an earlier state in the editing process. Here are a few of the more general commands to get you out of trouble, and make your life easier.
I botched an edit and need to go back to a previous version.
Oops, I went back too far.
There is a chain of blunders I need to back up from.
I've completely destroyed this image and can't undo back far enough.
Taking a shortcut using the keyboard might only save you a few seconds, but when you add up those seconds over hundreds of different operations and all of a sudden you've got quite a bit of extra time on your hands. This is a link to all of the default keyboard commands you can use with Photoshop CC. If you don't like these defaults you can set your own keyboard shortcuts. Go to Edit-->Keyboard Shortcuts.