Hydraulic car lifts work through the Pascal Principle, which states that any external pressure is distributed to all parts of the internal liquid and multiplied. The fluid in a hydraulic car lift is put under pressure by a piston on a control device which then forces that fluid and the pressure against a larger piston, which then lifts the car. The multiplication of the force and the static fluid pressure allows that lesser amount of pressure lift a larger amount of weight than would normally be possible.
The larger the vehicle or the heavier the weight determines the number of pistons that are needed to lift the vehicle. Despite the increase in force and pressure that is created with these sorts of lifts there are still limits on what the pressure can move. The distance between the first piston where the pressure is applied and the lift itself can play a role in how much it can lift.
A properly working lift needs to have the first piston a good distance from the lift itself. A hydraulic lift works very similarly to a lever, with a small force used to move a longer one over a distance. Many lifts like this are placed in the floor of the place they are being used at. This provides anchors and safety with keeping the load balanced.