I'm only familiar with the air suspension and hydraulic levelers that are on motorhomes (I believe electric versions also exist). The air levelers use the air suspension bags and inflate each as necessary to achieve level. Hydraulic levelers are hydraulic cylinders or "jacks" and are powered by a central pump or one pump per cylinder. Both automatic and manual versions exist (at least of the hydraulic types). The automatic levelers simply require a button push and they take care of everything (assuming not on impossibly sloped ground). The manual hydraulic levelers require the operator to push up/down buttons to achieve level.