15 years old ? flabby arms, smaller waist, thinner legs? please help?

Don't worry so much about how you look, but if this is serious, than I would advise CARDIO WORKOUTS. These are activities such as jumping jacks, jumping rope, running up and down stairs, running, and other activities that burn calories, but don't necessarily add muscle. Also, the easiest way to eat healthy is this: every time you want a snack that isn't healthy, replace it with a fruit (try to find fruits that are high in vitamins). Also, drink a lot of water, it will help.