Opening a Terminal session:
If you want a Root Terminal, first add it to the menu
For a regular Terminal, pick the "Applications" menu from the task bar, then the "Accessories" menu, then the "Terminal" option.

Exiting a Terminal session:
If you've got a "#" prompt, just type "exit".
If the session is busy running a command such as "nautilus" (the File Browser), close the File Browser first.