My pool either over fills or under fills:
The water leveler is in your deck, in a cement crock under a lid that looks like your skimmer lid. It operates in the same way as the standard toilet float. The float is "rough set" by your startup person but usually will require fine tuning by you. Place your thumb on top of the bar (to raise the water) or your finger on the bottom of the bar (to lower the water). With your other hand, gently grasp the float and bend the bar up (to raise the water) or down (to lower the water). You shouldn't need to bend it much. Bend just a little and give your pool 24 hours to reach it's new water level. If needed, do another minor adjustment.

My water leveler won't shut off:
Many areas have high water pressure that can force the water leveler open when it tries to close. Attached to a faucet (usually at the back or side of the house) there is a valve shaped like a flat bar. When the bar is parallel to the pipe it is all the way open, when 90 degrees (like a "T") it is closed. Close the valve completely and then barely open it until you can just hear the water flowing. This is usually enough to maintain proper water level in the pool and reduces the water pressure so the water leveler can close