A pressure side cleaner is attached to the pool via a hose to either a return jet (fed by the pool pump) or a dedicated port (usually fed by a separate booster pump) the pressure from the pump propels the cleaner & the debris it collects goes into a bag or a basket. An popular example is the Polaris 360.
A suction side cleaner is attached to the pool via a hose attached to the skimmer or a dedicated suction port & is propelled by the suction of the pump the debris it collects goes into the pool filter. Some examples are the zodiac mx6, the Hayward “pool cleaner/Poolvergnuegen”
wanda the whale, pentair kreepy krauly(there are multiple types of cleaner with this name).
Robotic cleaners are stand alone units that are powered by controller that plugs into a standard outlet. The debris they collect goes into a basket or a bag within the unit. They operate independently of any other pool equipment.