GE washer wont spin belt appears loose

GE washer won’t spin. I opened it up and found that the belt is loose and there is a pile of black belt rubber dust. Both pulleys turn freely. I easily removed the belt with my hand. It appears to me that the belt some how got loose and now needs to be replaced and the mechanism adjusted some how to tighten the belt. What happened and how do I fix it?

Gene,
So, you think its just a worn belt and not a bad clutch? Is there anything special about how to install a new belt? The worn one was so loose it came off easily.