If you're using a laptop or helping someone else use one, keep in mind that on most laptops the user will have to hold down the fn key (bottom-left corner of the keyboard) as well as all the other keys necessary to use VoiceOver. This can be a limiting factor for some people. But you can change that behavior:
Open the “Keyboard & Mouse” system preferences. Click the “Keyboard” tab and put a check in the box to “Use the F1–F12 keys to control software features.” See page 403 for an illustration.