Pop tends to have a more mellow beat than the others, and is typically "softer". Rock is very vague and can be described by anything that has screaming, lots of drumming, "heavy" bass, and lots of guitar riffs. Punk is usually "harder" than rock, so to speak, so you can expect a lot of anything you hear in rock music. But keep in mind that this is what they are to me. They could be completely different to someone else.

pop is more like bouncy, or light. and rock is like a huge party.... dancing and doing that whole air guitar thing and punk is like a milder verison. hope this helps:)