Double click the active tab to temporarily hide the ribbon and double click again to display.
This keytip displays the name of the command, the shortcut key if it has one and a short description
Every command on the ribbon also comes with a new shortcut. To invoke a command using the new ribbon shortcut key first press the Alt key to display the shortcut keys for each tab and also for the quick access toolbar. Then press the key for the tab you want and then press the key for the command you want.