Don't know how to start exercising?

Ok I don't know how to begin exercising, im not over weight or underweight but i have a lot of belly flab. everyday for the last few weeks i have been eating bars of chocolate and eating burgers and no exercise Iv had enough now i wanna get in shape. I got man boobs, a chubby belly and flabby arms. Im 17 years old how do i loose belly fat fast and get in shape. I dont have money for a gym so i need home exercises?