Definitely eat tons of calories, limit the junk food as mentioned before. Your metabolism will take care of you at your age, so don't worry about gaining fat. The excess calories will help you develop muscle, so you should not really be 'dieting' to lose weight. You may be curious about supplements, and all kinds of stuff that professional fighters/athletes are taking, right? I highly recommend you don't take anything more than a multivitamin (to fill in the gaps in your nutrition) and maybe some protein if you're not getting it in your food. This is a critical time for your body to develop, as others have already stated.
Obviously you are not overweight, so why do you feel the need to lose weight? Are you in any sports? If you're looking into beginning MMA, fast-paced endurance sports are a good idea, and I suggest some basic plyometrics. Don't worry about bench max, and all that stuff.