Hi, you are young and exercise for the first time always pains. I think you should start gradually. Start with some walking everyday like for 20 minutes and gradually increase to 45 minutes. Once you become a bit comfortable with it you can move to some cardio workouts(available in plenty on this app). Then when your body become use to exercising you should move to HIIT training. This will help you gradually lose weight and also keep it off. Don't forget to eat healthy and avoid junk food. Hope it helps.