A basic distortion sound from an amplifier is usually created by turning the gain knob up almost all the way and using the master volume to adjust your overall volume. The bass, treble and middle controls should be set half way to start, then raise or lower them to suit your taste.
Pedals can be used to create cool distortion sounds or to increase the distortion generated from the amplifier. Set your amp to a clean (non-distorted) sound by lowering the gain knob and raising the master volume knob, now you can add a distortion pedal to create your overall sound.
Overdrive pedals are one of my favorite's for adding more distortion to an amplifier that already has some distortion. I use my amp distortion sound mostly for rhythm then kick in the overdrive pedal for my leads, this adds more power and sustain to my sound.
John McCarthy is the creator of The Rock House Method and a leading innovator in the field of video lessons for musical instruments such as guitar, bass, keyboards, drums and vocals.