When going about getting a heavy rock and roll sound out of your amp, you need to set the right tones on it.

On your amp, you should have knobs labeled Gain, Post, Low, High, Shape (Mid), Bass and Treble. Low and High is also interchangeble with Bass and Treble if you dont have those knobs.

Set them to this:

Gain: Turn halfway from max
Low: Max
High: Max
Shape: a little over halfway
Post: Turn to your liking, post is volume.

If you have an amp like mine you have the same knobs for clean channel also. They should go like this for a nice warm tone:

Low: Max
High: Max
Mid:  2-3

Try it out and see what it sounds like. You will probably break away from this template later as you get better and use your own settings.