Start GNU Backgammon by running the program gnubg. Once started, it will process commands from the terminal.
You can also instruct @gnubg{} to read an existing match from a file, to play or analyse. (FIXME actually you can't yet, but you should be able to.) To read the match from filename, specify gnubg filename.
@gnubg{} will give you a short summary of how to invoke it if given the option @option{--help} (@option{-h} for short), and report its version with @option{--version} (@option{-v}).
GNU Backgammon will normally use a graphical board window under the X Window System, if possible. To prevent this behaviour and use standard terminal output instead, you can specify the @option{--tty} option (which can be abbreviated to @option{-t}).