As soon as you press ALT, you see little labels, or badges, pop up showing the Key Tips for all the tabs. After you press a key to activate a particular tab, the badges showing the Key Tips for the commands on that tab appear. In other words, you see only one layer of Key Tip badges at a time, and you must choose an option before you see any more.
Key Tips are a great way of using keyboard shortcuts, because you have a constant reminder on screen of what keys you need to press. No memorizing is necessary.
If you use a screen reader Key Tips should be available to your screen reader through a technology known as Microsoft Active Accessibility (MSAA).