If you have a flat butt and you want to make it round will the exercises make it hard?

Yes. Exercises will help. Especially squats. The butt muscles are some of the toughest to firm up. With dedication and hard work you can create definition and firmness. It will be a few months before you see any results although you'll feel results after a few days of doing squats. Its best to do weight training or resistance training (like squats) ever other day to give your muscles a rest. Genetics play a role in how your butt looks, also. If your Mom, Grandmother, etc. have flat butts, you will NEVER have a butt like JLo -- no matter HOW hard you exercise.