What is the significance of Undo and Redo button?

The Undo feature can quickly correct mistakes that we make in a worksheet. When we want to reverse our last action in a worksheet, we click on 'Undo' button.

The Redo button lets us perform the previous task by using 'Undo'. It changes in response to whatever action we just took. The 'Redo' button becomes active whenever we use 'Undo' button.