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 Section 13.3. It works on key-combinations, you type
On the command-line to begin. Now you start with one virtual terminal by default, but using the key combination CTRL-A and then hitting "C" you can create another virtual terminal to use.
Use CTRL-N to go to the next virtual terminal and CTRL-P to go to the previous virtual terminal. Also try hitting CTRL-A to go backwards and forwards between two particular terminals.
screen also has various other abilities that you can test out. The documentation and guides are well written so please feel free to read the manual page or try searching the internet.