Answer:
Start an exercise routine, the sooner the better. If you nip it in the butt now, you will have a nice conditioned body for when you get to be an adult. Always try to do a little work. I let myself go once and it is hard to try to pick up the pieces.
if you think you are get a little fluffy. Then try to limit you junk food eat a little bit healther. and exercise. you can do sit ups, walking around the block, walk your dog if you have one, or even ride your bike. If you do this daily. then i guarantee you that your fluffiness will come off soon.
definetly start an excersize program. find exercises that fit your energy level and that you enjoy. as you progess, you may go into more difficult levels of your program. be sure to mix your weight training with cardio.
Just do general exercises. Don't watch as much tv. Go for walks, that's an easy way to keep yourself fit. CUT DOWN ON JUNKFOOD and SODA! SODA is huge for fat calories. Plus, realize if you're a teen, your hormones are probably going to be raging. Your body will be constantly changing from early to late teens.