How do I change the default configuration of MPlayer movie player?

[Steven Vollom]

>  ~/.mplayer$ cat config
>  # Write your default config options here!
>  lirc ="no"
>  joystick="no"
>  cache="8192"
>  double="yes"

This will be my first time typing in an instruction where I don't use a GUI.  
If I want 16:9 aspect ratio, do I just type in:   16:9="yes", or do I type in 
aspect ratio 16:9="yes"?  Thank You.

Steven