Just Like Your Vacuum Cleaner at Home
Pool vacuum cleaners are attached to the water pump and filtration system of the pool. Once in place, the suction stops going directly through the filter and instead goes through the vacuum head and up the flexible hose until it finally reaches the filtration system. In this way, you can clean the bottom and sides of the pool rather than just filtering the water itself. The vacuum head is attached to a sturdy fiberglass handle so that it can be pushed around much like a regular home vacuum cleaner.
Dirt and Refuse Are Gone
The suction comes from the filter that normally pulls in water, filters it and returns it to the main body of water anyway. By using this suction and sliding the vacuum head across the floor of the pool, you can scuff up the grunge (dead leaves, bugs, loose dirt). The dirt and refuse will be caught in the pool's filter, which must be cleaned out with a garden hose later on.
Vacuum Regularly in Season
Pool vacuuming should be done on a regular basis, at least once or twice a month, during the pool season. Preferably it should be done once a week because the water will get stuff in it no matter how hard you try to keep it clean. This is just another way to maintain the cleanliness of your pool, much like filtering and pH balancing the water and adding chlorine when needed. None of these things need to be done every single day.