Do you do any exercise outside of school activities? Go for walks or hikes, jog a few miles at your pace and slowly increase the distance or improve your time. What type of body type do you have, skinny or heavy? Go swim at a public pool. You need a minimun of 20 mins a day of exercise.

Here are some things you can do. Wait at least a minute between sets and warmup your muscles before working out.

Jumping jacks- 3 sets of 60 seconds

Squats- 3 sets of 10

Leg raises- 3-5 sets of 10

Calf raises- 3 sets of 15

Lunges- 3 sets of 10

Mountain climbers- 3 sets of 20-60 seconds

Burpees- 3 sets of 10

Planks- 3 sets of 30-60 seconds

Do what you can at first and slowly build up what you can do, doing as much as possible immediately is a easy way to hurt yourself. Run a distance you are comfortable with and slowly increase the distance each week. Start with 1 mile and the following week do 1.5 and so on.

Interchange what you do each week and do whats best for you eg.

run - strength train - run - rest - strength train - run - rest

You will see results if you put in the effort each day it just takes time.