Start with bodyweight exercises. It boggles my mind that no one on this "fitness site" mentions them.
If you're just starting out try this. A pyramid work out of nothing but bodyweight exercises. It is a combines resistance and cardio work out.
You do squats, push ups, crunches, and pull ups. if you can't do pull ups try a body row.
You will do each set of four exercises with no break between exercises. your reps work like this.
1 squat, 1 PU, 1 crunch, 1 pull up 30 sec rest.
The 2 of each, then 3 of each etc up to 10 of each
you are now at the top of the pyramid rest 1 minute then go down
9 of each, 8,7,6 down to one.
when you're done you will have done 100 reps of each.
After you can do this start changing exercises, add lunges, dive bombers, etc etc etc.
Then you can start doubling the pyramid 2,4,6,8,10 up to 20 and down
When you're doing 500 squats and 300 push ups and 200 pull ups a day you are officially a stud.