Notes

It won't be easy to break some habits, you have to be ready for that. It requires work. Long story short, you have to eat high protein food, like eggs, beans, fish and forget about carbohydrates, especially fast carbs, so no bread, or anything sweet at all. Maybe some fruit in moderate amounts. And power exercises in the gym. Not eating is very bad. You have to eat. Just eat right and healthy food. No processed food at all. And like I said, nothing sweet, no bread, no sweet drinks like cola. But feel free to have a steak. And it is not fatty foods that you should avoid, nothing wrong with some fat, it is carbohydrates that make you gain mass. Any meat is basically protein and some fat. Well, ease off on weed then, munches will ruin hard work. If you are serious about it, I'd through all your sweets and bread in the dumpster right now. Think of them as poison. As for exercises, you start with fast walking on treadmill watching your pulse to build up your stamina. Do not run, that will fuck up your knees. Also there is this machine that works like walking yup the stairs constantly, that is even better as a start. Once you get into the groove, squats is another thing you do. There is plenty of info in the internet on how to do them right, just look it up. Build up the weights gradually. Don't throw them away of they are not yours, but put a total mental block on that. This shouldn't be food to you. Not something you can eat under any circumstances. This applies to any carb heavy foods. This will take some getting used to. For a month or so this will be painful.
You will get cravings. Drink water, masturbate, go for walks, anything, but don't eat that. After about a month your body will get used to it and you'll be fine again. And in about 2 months you will see very noticeable difference. And after that it will be easier because you will see clear results. It will motivate you. But the first month will be torture and another month will be kinda "does it even work" kind of thing. Gym 2-4 times a week is very important as well. Especially power exercises. The reason for that is that your body will consume muscle first once your calorie intake goes down, unless you do power training. So without the gym you will just get weaker and fat won't be consumed. If you train, it will eat the fat first. And you do not have to starve yourself, but your meals should be moderate. Basically greens and some protein for the muscles. Vitamins too. But I repeat this again, forget about anything sweet or bread. No junk food at all and no processed food at all. I hope you endure that. :) But good news is that this is not hopeless, especially at your age. In a way, it is easy, because you just have to follow the rules and results will inevitably come. Also, if you have somebody, suck as much cock as you can. This will help with depression and cravings. Let them know that you are not ok with their eating habits and cook for yourself. If you can rally them to change as well, great. If they refuse, just do what you must. Depression is a real bitch to deal with. Thing is, the only way to win here is doing what you must, even when you feel like you can't any more. You just drag your sorry ass to the gym, mindlessly and do what you must. Same with food, you just condition yourself not to and just press on. It might feel unbearable, but after a while you will see glimpses of pleasure in it until one day you will find that you find pleasure in healthy lifestyle. You can also punish yourself. Feel a craving to say "fuck it all and smoke weed?" 20 squats right there. So a lot of it in the beginning is tricking yourself. But good news is that it gets much easier after a while and eventually becomes fun. :) For you for now squats is the mainstay for you. Eventually you will do other exercises, but not in your current state. I don't want you to damage your spine or knees. As long as you go. Look up how to do squats properly first. And you start with an empty bar. No weights, just the bar for the first 3 visits. Work on proper form. Very important to avoid trauma. And bring up the weights gradually. You aim for 5 sets of 8-12 reps for now with the weight. Later on you will do heavier weights and less reps, but you start with that. And self-punishment is done without any weights, so 20 is about the right number. Oh, and your legs will hurt as fuck for the first 3 days. To help with that, stretch and then go to the gym again. This will help with the pain. Just an empty full size bar that is used for squats/bench press. I believe it is around 40 lbs. Or actually... the very first time (today) you can do it at home with no bar. This will help your muscles a bit, won't be as painful. Oh, and you do not power workout on the same muscles every day. Rest for 1-2 days. But you can do cardio daily, this is up to you. Cardio is good, it helps, but it is not absolute must as such (except like 5-10 min warm up before power training.) STAY HYDRATED!!!!!!!