Using the key combination ALT-F* keys you may change to different virtual terminals. You will have several (usually 6) virtual terminals setup with shells. Number 7 is usually setup with X you need to use CTRL-ALT-F* to change to a terminal from within X (X as in the X windowing system).
is a great program that allows you to switch between multiple virtual terminals on the one physical terminal that you are using. Its a command-line based window manager, clearly this isn't that useful if you do have virtual terminals, but its amazingly useful when you log into machines remotely, using ssh and similar, see the Section called Remote Administration Related in Chapter 13. It works on key-combinations, you type