Re: Combo to Cab
Plus if you plug it into the headphone jack there will be hardly any sound - the headphone jack only puts out enough electricity for the speakers in headphones, so you'll have to get some duct tape and attach the cab to your head to hear it...
If it's a combo, there should be a spot where the speaker plugs into the amp part of the combo - find that, unplug the speaker in the combo, plug the cab in and you now have sound coming out of the cab instead of the combo speaker.