Once your scope has been mounted, you need to set it up for your eyes. First, ensure the rifle is unloaded and insert a chamber flag. Close the bolt, if necessary, to keep the chamber flag in place.
Close your eyes and relax. Point the rifle at a neutral background such as a cloudy sky or a blank wall. Open your eyes just long enough to determine if the reticle (cross hair) is in focus or not.
Do not spend too much time looking - your eyes will strain to bring the reticle into focus and that is not the goal. Only open your eyes long enough to determine if the reticle is in focus or not. Close your eyes as quickly as possible.
Use the outer ring (usually marked with - 0 + ) to make focal adjustments to the reticle. Repeat this process until when you open your eyes the reticle is in focus.
If you have a lock ring, tighten it against the eye piece to prevent the focus from changing.
A fixed objective scope will generally be set at between 50 and 100 yards (see your scope manual for specifics). This means only targets at that range will be in proper focus. Targets closer or further out may appear fuzzy.
Some scopes have an adjustable objective (AO). This allows you to bring the target into focus.
Adjustments can be on the front, rear or side of the optic. Look for distance marks such as 25y, 50y, 100y all the way to infinity.
Ignore the distance markers and simply turn the adjustment until your target is in focus. Remember to rest your eyes during this process or your eyes will strain trying to bring the target into focus.
AO scopes are highly recommended for shooters with bi-focal's and/or astigmatism.