yamamama

My sons 2000 yamaha warrior will not start. It will turn over but not fire. There is no spark @ the Spark plug. I can pull it off and it runs great. I tested the stator and the ohms were very low on one of the plugs. should i test anything else?? and if so how??? (i will apoloize in advance...i may not know the proper names of some parts..I have never done anything like this....I'm just a mom trying to fix sons bike...if i can.