If you want to use the theoretical approach, you can do it like this:
You set your custom goals (calories and protein)
You fill out these goal numbers into an app or website like myfitnesspal or fatsecret. Any calorie & macro tracking app that allows you to outline your own custom goals should work well enough.
You hit your goals daily
This is how macro-tracking people do it. They set their goals and they try to hit them as closely as possible every day. That’s all there is to it.
Whichever way you choose to lose fat, it is good for you to know as much as possible about your nutrition. You need to know which macronutrients are which.
That’s why I will still recommend you learn about calories and macronutrients. I do not, however, recommend the super strict approach where you hit a specific number of fats and carbs.
Tracking calories and protein is one thing, but needing to hit your fats and carbs is not necessary: as it’s already been proven it doesn’t matter as long as you hit calories and protein, you don’t need to worry about hitting the same numbers of fats and carbs.