Simply speaking, swimming pools are just big basins of water, and regardless of shape and size, they all generally work in the same way. They use a combination of filtration and chemicals to continually clean a large volume of water.
In the most basic terms the way a pool works is, water is pumped in a continual cycle, from the pool (starting at the main drain), through the filter, heater, chemical treatment system (i.e. chlorinator or FROG® Mineral System), and back into the pool again. This continuous cycling of the water through a filter and chemical treatment system helps keep the water in the pool free of dirt, debris and bacteria. Some pools also include a heater to keep the water at a desirable temperature.
A swimming pool typically needs these ten major components to function continuously: