The “undo” button is pretty self-explanatory. It works the same way as on the other programs. It lets you go back on and restore previous designs or edit.
The history button works similarly, though it has few differences. For a start, it shows the exact date of the recent change and lets you move back and forth through the changes. That would affect not only the particular design but also the design editor’s changes, e.g. if you changed templates – that will be registered.