Why can't I change the oil in my Craftsman 18" chainsaw?

This is my first chainsaw, and I’ve looked in the owner’s manual that came with it but I can’t find instructions on how to change the oil in my craftsman chainsaw.

Is there something unique about craftsman chainsaws that I don’t know about? I constantly have to put oil in it to lubricate the chain; does the bar & chain oil work in the motor?