I think he means using the face of the cylinder in a concentric mate to the hole in the material (see image). Then you would mate the face of the under side of the screw head to the face of the part / material being fastened (see second image). As far as "Simplified" assemblies go, he talks about removing interior components or suppressing them if they're not visible in the view you're creating. You would also suppress things like text on the model.
Thank you for the information. That is a good tip. I always have problem with parts that are suppressed. I use hide instead.