As mentioned earlier, vi is one of UNIX's typical editors. It is probably present on all modern UNIX's, and it is actually a visual interface on the `ex line editor. The command mode of vi and ex are the same. If you know in advance that you will not be making changes to a file, you can either invoke the editor with the ``-R'' switch, or call it by the name view.
As mentioned before, vi is a moded editor. To get out of data mode, you hit the ESCape key. Hitting it twice (with a beep on the second press) will more or less guarantee you are out of data mode. To issue a bottom-line command (ex), you hit the (full) colon ``:'' key, followed by the command you wish to execute.