DO I NEED TO GROOM MY GUINEA PIG?

You do if the guinea pig is a long haired variety. In most long haired guinea pigs the hair growth on the rear end is long so the undercoat does have to be trimmed back. If it isn’t then it will quickly become soiled and knotted. Ask a guinea pig breeder to show you how to do it.
Guinea pig expert Peter Gurney recommended standing the sows, the females, on a towel and holding them steady with the left hand on their backs. Un-neutered males should be trimmed on a towel on your lap with your left hand cupping their testicles. This is to make sure you don’t cut them by mistake.