How much weight do you want to lose before school starts? Safe weight loss is 1-2 pounds/week, so the most you should plan on is 10-12 pounds, if you stick with a pretty strict diet and exercise routine, but that's a good start and if you stay with it, after school starts, you can really make progress over time.
There are numerous exercises for belly fat, such as crunches, leg lifts, even brisk walking. Try searching YouTube for "how to" videos.
I think you should create an exercising timetable and weight loss chart. Give yourself projects to complete before going back to school like the 30 day abs challenge :).
Green tea boosts metabolism.
Only do exercises you enjoy. Eat healthy delicious foods to feel satisfied and most importantly get your heart rate up.
Skipping burns more calories than jogging.
You start to burn fat about half an hour into a good workout. Good luck, and enjoy seeing your body change and your confidence boom.
It isn't easy and when you see results you will want to do exercise instead of seeing it as a chore.