im 14 years old and my dad signed me and him up for a gym throughout the summer which i think is a really good idea for me cause i rlly need to loose weight..i have a healthy diet already but never backed it up with the exercise what exercise should i do when i go to the gym? how many days a week? how long? help plzz thankss........im14 5 foot 10 and weigh 195lbs =\