A winter cover is designed to protect the pool during the winter months when many above ground pools are not in use. It is basically a tarp with grommets around the perimeter and comes with a cable and winch to hold it in place. To install an above ground pool winter cover, you would first want to make sure all of your other winterizing has been completed. This would include cleaning the pool, lowering the water level below the return fitting and skimmer, and adding pool winterizing chemicals. Basically, make sure anything that requires access to the pool water is done so you won't have the hassle of having to remove the cover. If you are using an air pillow under the winter cover, inflate and place it in the center of the pool right before you put the cover on.