Exercise is never a waste of time. It will benefit you in many ways whether you are overweight or skinny. You are correct though that you'll need to reduce your bodyfat for the benefits of exercise to physically show. For that it's all about diet. You need to eat healthily and not too much. To get started just cut out all the extra sugar and reduce your other processed carbs. So, no soda, candy, cake, ice cream, cereal, etc. and reduce things like bread. Increase the amount of vegetables you eat and for sweetness eat fruit. Another really good thing to eat is eggs, as many as you want. Eggs are a nearly nutritionally perfect food for humans. Be sure to eat the yolk too as that's where most of the good stuff is. If you are hungry then more vegetables help fill you up and more protein like milk, meat, cheese, nuts, etc. help turn off the hunger signals.
I would recommend getting your diet nutritionally sound as described above first and only then worry about counting calories. Also, since I assume you are still in puberty, DO NOT cut your calories too much. You need both the calories and the nutrition for your body to grow properly. If you cut calories too much and starve yourself during puberty you can screw yourself up for life.
For exercise your goal is to develop more musculature. For that you need to do strength training. For muscles to grow you need food; another good reason not to cut calories too much.
For strength training heavy weights such as powerlifting is best if you have an equipped gym available. If not then bodyweight exercises are also good and can be done by anyone anywhere. Do not get discouraged if you don't see the results you want in the first week or first month. It takes time, many months. Also, you can build a tremendous amount of strength without testosterone. You can be stronger than most men you see walking around. Testosterone is not needed for that. What you cannot do is build a huge bodybuilder type physique without testosterone. You can get massively strong but not massively big. The reason is because muscle size is only one factor of many in strength and those other factors are more important than size.
You should also start doing some sort of cardiovascular exercise every day. Walking is very good. When you feel like it you can run some, cycle if you have a bike, or swim if you have a pool. This, alongside a better diet will help burn away fat to reveal the hard work you are putting in. The muscle you build will also burn more calories all the time further helping your fat loss efforts.
If you are working out hard you need to sleep, at least seven to eight hours, or more, every night. This has the added benefit of reducing stress hormones that cause your body to store fat.
If any of this helps and you have any questions Then I would be happy to answer them. [emoji846]
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