How to get guinea pig to stop biting ?

Piggies don't bite unless they are scared and you grab them.

They need to chew for healthy teeth, might take a finger or hand as something like that.

See they have plenty of hay always, that should limit trying to chew hands.

You know, piggies are very social and really should be kept in pairs or more to be happy.

One bit of advice is don't chase or grab them with hands, give them hides and let thm avoid you if they choose. That freedom makes them at least feel safe with you and may come to you in time to cuddle next to you or climb onto a lap, they like their feet on the ground and hate being picked up, ab bit like rabbits.

Guinea pigs must live in pairs (one female and one neutered make is the least likely to fight) or herds.They can not live happily alone unless the vet says They are a special case who require such.

 They need 8 square feet of floor space each, so cages you buy are normally too small. You can buy c&c panels and make your own large cage for a low price. They need safe bedding, either fleece or paper/aspen/hemp based ones. They should be spot cleaned every few days and fully cleaned every 2 weeks or so. 

Some guinea pigs will bite out of fear, so announce yourself first and if you want to pick them up make sure they can see your hands so it isn't so scary (they don't like being picked up anyway). He will need access to hay at all times, and be fed pellets and veggies twice a day.

I suggest watching ErinsArk on youtube, but if you don't meet the bare needs be will continue to bite.