The terminal is where everything gets done in linux.
So if this is true?
How can I start a .avi extension file format from the Terminal?
In general you start any command from a terminal by entering the command.
So to edit a file with gedit
An .avi is no different, just a different command
You may use any media player you wish.
the only thing is an avi itself is a container, so you may need to install some codics. codics are the tools to play mp3 and other audio visual files.
this link may help