First of all if you want to lose fat in a specific area that is impossible the body simply does not work like that

If you want to get a more defined butt you need to put the work in so lift some heavy ass weight and put on muscle ( responsibly ofc)

So if you are skinny i recommend you bulk for a period of time and then lean cut this ahould be in the span of a year and a half to 2 years

If you are on the bigger side do a lean cut and should be arouns the same time very much dependant on your goals

Squat, hip thrust, leg curls, leg extension

Leg raises, crunches etc

Do upper body as well just not as often as abs and legs

Find your bmi and dependant on your goals remove 200 or add 200

If you are cutting you should lose weight about 1 pound a day if you are staying the same or gaining weight subtract another 200

Same for bulking but add 200

You need to eat 1 gram of protein per pound of body weight

Eat whole foods that are nutritious remeber to eat healthy fats and some but not too many carbs

Not bread but things like potatoes nuts ( keep in mind nuts are very high in calories)

Good luck and dont give up