Theres always a lot of how do I start questions, so I'm copying and pasting this from a previous post.
To maintain weight
calories in has to equal
calories burned. To lose weight you need to create a calorie deficit. A
pound of
fat is 3500
calories, so to lose 2
pounds of
fat (doctor recommended max per week) you need to get rid of 7000
calories a week. How do you do that? Well many people suggest splitting it up by reducing your maintenance intake by 500
calories and then working out and burning 500
calories each day. That allows for a 1000 calorie deficit a day.
To get a six-pack, or toned you have to understand being toned comes from losing
fat and once that layer is diminished you can better see the muscle underneath. You can't build muscle too effectively as you
diet, but weight training and calisthenics will help you preserve muscle tissue while your
body breaks down
fat.
I hope that makes sense to you. Also talk to your doctor about figuring out a proper minimum calorie intake, as you're still growing so you don't want to risk cutting it too low.