The first situation: If you are a fat man with a high body fat rate and want to have a perfect figure, you must first lose fat and let your body fat rate drop to a certain range before you start to gain muscle. It should be noted that your body fat must be reduced to a certain range, otherwise you will be very painful when you gain muscle, because you can't see the outline of the muscle at all, and you can't see the result of your efforts, which may make you lose confidence or even give up. Reducing fat is a very painful thing. If you want to lose fat, you must do a lot of aerobic exercise. Jogging and cycling are good choices, and the time must be controlled for more than 40 minutes to be effective. Be sure to stick to it and get into the habit, otherwise it will rebound.
The second situation: if your body fat rate is not high, but you don't have a body shape, you can gain muscle directly if you want to perfect your body. Systematic muscle building training is enough. In this case, all you need is a fitness card and a persistent heart. Remember not to get addicted and practice yourself as a "muscle freak".
The third situation: this is also the worst one. There is a kind of people called "muscle fat". Their body fat is low, but their weight is heavy. If you belong to this category, congratulations, your pain and your nightmare will haunt you for a long time. This kind of person wants to have a perfect figure, just like the Long March, which has a long way to go!
This is my view of reducing fat and increasing muscle. I hope it helps you.