Its ich, or white spot, can kill them if not treated, go to your local store and ask, its no prblem once you get some treament, dont panic, very common
Do the spots look like grains of salt? If so, then probably ich. Personally, I would use the salt/heat treatment with ich. Here is a great article from the articles section of this site on how to treat ich: Identifying and Treating Ich. I hope it can help you.