1.)I keep hearing different places advertising "only 1 net carb!!" or impact carb.

what is the difference of a "net carb", "impact carb", or just a regular carb?

2.) also, I know carbs serve as energy for the body. Also that if I don't get enough carbs my body will seek out alternative energy sources, starting with protien. My question is, do carbs play any other role in building muscle?