Unknown snake

Hello, It would appear to be some sort of garter snake or other small colubrid (garters, corn snakes, milk snakes, ect.) Without knowing what county and state, its very difficult to tell species with just a picture. Try offering it small gold fish or earthworms. After you get it feeding you'll either want to get it trained to eat pinky mice or dust the tail of its food with vitamin powder so it will have a complete diet, you won't need to dust the pinkies because they provide all essential nutrients.