Get access to some weights and start lifting. There are lots of books and magazines out there to give you basic exercises for each muscle group. Most gyms that you go to should have a basic push/pull routine for anybody who is in need of one. Make sure your diet is clean and high in protein to help muscle growth. The more you read and research, you will be able to tailor your specific routine and diet to your needs. You need to know your goals to do this. Are you wanting to compete, just get fit, or what?