How to get stronger?

There's a lot you can do with just your body weight to get a full body workout:

Chest - Push-ups (put your feet up on a chair or couch to up the intensity)

Back - Pull-ups (if you have something you can hold on to)

Core - crunches, planks, supermans

Legs - squats, lunges, wall squats, plyometrics

Triceps - dips (just use a chair), push ups with your hands close together

Shoulders - pike presses

Use their ^ advice for the excersises(push ups, sit ups, etc.) but on top of that, eat lots of lean protein and less fat or it will be hard to build up muscle.

pushups, crunches, squats, wall sits, etc. There are websites that show you which exercises work for different areas.