How to access the Ribbon using keyboard in Excel 2007?

To access the Ribbon using keyboard, press the ALT key. You will see some characters and numbers with a border surrounding it. The characters or numbers are the ones you need to follow to access the commands in the Ribbon.
For example, to access the New Comment command which is in the Review tab, press the ALT key and press R, and finally press C (ALT + R + C).