Basic Open Sighting
Open sights are a form of iron sighting with a front sight and a rear sight. The front sight consists of a metal blade on the end of the barrel, called a post, or a post with a bead on the top. The rear sight consists of a plate with a notch in it. The rifle is sighted by aligning the top or bead of the front sight so that only it is visible with a bit of daylight on either side.
Manually Adjusting Open Sights
Open sighting systems can be rudimentary and have no means for mechanical adjustment. This means the shooter must be old fashioned and estimate for himself what adjustments need to be made for windage and bullet drop. Bullet drop can be compensated by aiming higher and windage by aiming in the direction opposite that of the wind. Both of these should be small adjustments, but learning how to do this can only be achieved with plenty of practice.
Mechanically Adjusting Open Sights
Many open sights do have mechanical aids for adjusting the rear sight to compensate for bullet drop. These take the form of either a slider or dial that raises the rear sight to a corresponding range. Much more rare, complicated and fragile are adjustable sights with controls for windage and even bullet weight.