Weird noises
 

I'm new to mountain biking and just bought a gt avalanche 2.0. The first time I went out and rode it something makes a sound like metal rubbing against metal, and every time I pedal hard on the right side, something makes a loud clicking sound. I've already brought back to the shop I bought it from to get it fixed, but it didn't help. I really don't think they know what they are doing considering the fact that after they said my bike was ready to ride, the crank fell off within 15 minutes of riding. Does anybody know how I can fix these noises or are they normal? Any help would be appreciated.

Could be anything, but...

Metal against metal sound may be the chain rubbing against the front derailleur. Check that it's adjusted properly (http://sheldonbrown.com/derailer-adjustment.html), or find an LBS you have more confidence in.

The clicking? Could be a loose bottom bracket, or dirt in the threads of the BB. Needs to be well greased. Or it could be the crank arm. What do you mean the crank fell off? If the arm fell off the spindle, you may have damaged the spindle hole in the process. If that's the case, I'd get a replacement from that shop, and have some other shop install it, or install it yourself.