I'd suggest starting with a basic basic routine. And since you don't really have any equipment, you could start with calisthenics.
Like do 20 - 30 pushups, 20 - 30 situps, as many pullups as you can muster, 10 - 20 lunges and 10 - 20 squats. it's an extremely basic routine, but if you're worried about overdoing it, it's good to start low. Do something along these lines every other day until your muscles adjust to it. Then ramp it up from there.
As for a diet, make sure you're eating some sort of fruits and vegetables each day. Drop the sodas and start drinking water.
As I said this stuff is basic. If you want quicker, more effective and probably better results and advice, I'd suggest going to a gym and getting set up with a PT.
Good luck, man (maybe start a training log so we can encourage you along the way).