Basically there are three types of cleaners - suction side cleaners, pressure side cleaners and electronic robots. The difference is where they are powered from.
A suction side cleaner uses the suction power of either the skimmer or a dedicated vacuum line to drive it. Water flowing into the suction cleaner causes it to move and debris is moved into the cleaner along with the water. One usually uses an inline leaf canister to trap the larger debris so it doesn't plug up the PVC line. Suction lines are connected to the suction side of the pump and usually require a shut off valve to throttle the flow.
Pressure side cleaners get their power from the pressure side (discharge side) of the pump. They require a dedicated PVC line to the pool which is usually a smaller diameter than standard return lines. Also, because the discharge side of the pump has to push water through filters, heaters, etc, only a fractional amount of the water is usually drawn off the discharge side of the pump (before or after the filter using a smaller diameter pipe) and run through a booster pump to increase pressure and flow at the pool side port. Pressure side cleaners get their power from this high velocity water flow created by the booster pump and you can think of them like miniature power washers driving all around the pool and forcing debris up through a leaf bag.
Finally, robots are totally separate from the pumping system and derive their power from an electrical outlet. You simply plug them in, throw them in the pool and they do the rest. They have onboard motors and pumps to do all the vacuuming and moving in the pool.
No matter what you get, you still have to manually vacuum your pool. For that, most people will hook a hose up to the skimmer and vacuum that way. If you are a suction side cleaner owner, then you can use your dedicated vacuum port instead of the skimmer.
Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006