does anyone know any good and tiring exercises i can do to lose weight and gain muscle. i am 15 and fairly fat. i want some good mental training aswell so

i dont lose focus and the urge to workout. i have done some workouts in the past and everytime (the same with sports) i just lose the urge to do it and go play my computer. i really want to get healthier and have a balenced diet. thank you in advance for all

ur replies and help