Make sure your parents know what your doing. Starting any type of diet that young, should be made awear to the parents for proper guidelines.
Try eating maybe 5 small meals a day. Make sure you always have breakfast, because people who eat breakfast tend to lose more weight then people who skip it. Try staying away from soda and any drink that contains calories. Drink water, or iced tea with no sugar or maybe some green tea. Lipton makes a great diet green tea with citrus, it tastes really great. Also, stay away from the junk food and get your mom or dad to buy some of those 100 calorie snack packs. They come in chips, cookies and candies. Try walking everyday for maybe like 30 mins and then increase it to 1 hour on the weekends. Thats all I do and I so far am down 60lbs just from the walking and watching what I eat.
Always remember, diets can be fun. You don't have to cut all the junk food out. I generally watch what I consume during the week and then on the weekends I can reward myself with a nice desert or coffee drink the way i like it. You can still go out with friends to a nice restaurant (or Applebees or Outback) and still eat what you want. It's all about portion control, and thats what I've learned to do.
Great breakfast options: oatmeal, high fiber ceral (makes you full longer), multigrain waffles, eggs (cooked in Pam fate free spray).
Lunch options: 1 slice of pizza, turkey on whole wheat (add some fat free mayo, or some cucumber slices), soup (Campbells makes great healthy request selections).
Dinner: Is my hard point, my family cooks. So just cut the portions in half and you will be fine.
Also don't be afraid of going to the doctor. You might want to have your thyroid checked out to make sure it is not affecting your weight.
Good luck!
Don't forget, it's not just the calories, but what you are eating too. I thought they taught nutrition in school nowadays.............they didn't in the stone age when I went. But is there someone at school you can talk to as well? Maybe a science teacher, nurse, or home economics teacher? Even a counselor at school might have a suggestion.
Good luck and keep us posted.
You could talk to your mom (or guardian) and have her help you or maybe you could visit a dietician to help you out.
Or as pink suggested google calorie counter and a lot of sites will come up that you can go to. I also agree that tracking the food you eat is helpful. There are also a lot of sites on which you can do that. fitday.com is one, ***********.com is another and will also help you calculate your necessary calories AND has lots of fitness tips, examples of exercise routines, etc.
Keep posting and let us know how you are doing. ok?
google calorie calculator and that way you can figure out how many calories u should be eating... also keep track of your calories at a place like www.fitday.com