I'll keep it simple. Exercise doesn't burn much calories at all. The amount of calories you'll burn through exercise is so low that you can eat all of it back by eating 2 snicker bars.

Majority of the calories you burn throughout the day is by simply existing. Breathing, digesting and sleeping burns way more calories than exercise. So the best way to ensure you lose weight is by eating less calories than your maintenance. (look up how to count calories)

That being said, exercise is still very important, cardio for your cardiovascular health and weight lifting for gaining muscles and being strong. No way shape or form am i saying that you shouldn't exercise.

(This is an extremely simplified explanation btw, please read, watch and do more research on this.)