Although Ctrl + Z will undo most all commands before you save a file, if you accidentally undo too much you can always use Ctrl+Y to redo the undos in reverse order.
Ctrl+Z
Ctrl+C is a keyboard shortcut for 'Copy'. Ctrl+V is the shortcut for 'Paste'. Ctrl+X does 'Cut', and Ctrl+Z does 'Undo'. Alt+Tab switches between windows.
There are many different ways to Undo in Photoshop. Ctrl + Z is keyboard shortcut for Undo last operation, Ctrl + Alt + Z is Undo keyboard shortcut. You can Undo and from Edit > Undo or from HISTORY panel (Window > History).
Ctrl + C
F8
Press the windows key.
Ctrl + V
Windows Key + Tab
crtl-c
Windows key or Ctrl + Esc
ALT+TAB
The windows flag, on the bottom lower left side
Shift - F10