i have a problem with my bike. every so often when riding the cranks seem to slip and jolt forward. They also make a cracking sound when this happens. The cracking sound varies from a barely audible click to a full blown crack depending on how much pressure is on the pedals. How can i stop this?
There are no silly questions. If the bike's not working right, it's not working right.
Here's my advise:
Walk; do not run,do not ride the bike, but walk the bike to the bike shop where you made the purchase. If you have a loose crank arm, you do not want to strip it, so don't ride until it is fixed.
(I am assuming the bike is relatively new.). We are no longer in the prime biking season, so chances are they are not that busy. Ask if you can watch (oooo, kinky) and learn the cause and how to make the repair yourself next time. (don't be afraid to ask questions. There are no dumb questions. Either you know or you don't. No one teaches this stuff in school, so how else are you going to learn if you don't ask.)