How do you use a solar cover on a swimming pool?

There are two main types of solar covers for swimming pools. One is a solar ring which lays on the pool and has magnets around the edges to easily hook two or more together. A common brand name is the Solar Sun Ring.

Another option is a solar blanket that would work much like a rain cover or tarp at a baseball stadium. It would be rolled up on a solar reel and then unrolled across the pool when the pool was not in use.

Here's a few examples:

http://shop.bluehaven.com/lp-general-solar-blankets