Ok- I am going to tell you how to sight in your AR-15.   Military Matt at the range helped me.  First you need the right tools.  You will need a tool that adjusts the front sight.  It will allow you to raise and lower the front sight pin. If you are at the range ask the shop to borrow one- most likely once you have your rifle sighted you will not need it again.  

On your rifle near the rear sight you will have a knob that adjusts the sight from left to right. Make sure that it is centered.  You will also have a wheel that adjusts the rear sight up and down. Make sure that is on Z.  Next set a tall target that is 25 yards out. Not more and not less.  Take a sitting position and rest your rifle on a steady rest. Take your time on 3 shots aiming at the center of the target.  Review your bullet holes and adjust your front sight only.  For every inch from the center adjust accordingly.  Turn your front sight to the right if you are above target.  Turn it to the left if you are below target.   We were able to sight my rifle in 15 shots.

Once your rifle is sighted in you will have so much more fun at the range and spend less money on Amo when you practice.