Sight alignment is the process of properly lining up the eye with the rear and front sights on open or aperture sights. The sight picture is the image you see when the sights are aligned correctly with the target. To ensure that the bullet will travel to the target in your sight, it’s necessary to sight-in your rifle. Before you can do that, you need to determine your dominant or "master" eye.
With an open sight, you line up the target with the blade or bead of the front sight within the notch of the rear sight.
With an aperture sight, you line up the target so that the front sight is within the rear peephole.
With a telescopic sight with a crosshair reticle, you line up the target with the crosshairs of the sight.
With a telescopic sight with a dot reticle, you line up the target with the dot of the sight. The dot must be centered.