Many spas filter the water before it reaches other components. The spa pump may be located before the filter or after. Some spas have more than one pump, and a pump may have 2 speeds. Your spa may also be equipped with an air blower that can provide a tingling flow of air bubbles up through the bottom of the spa, or mixed in jets. It may or may not be located near the pump.
Many spas have adjustable topside air controls, which introduce air into the jets.
This is also a convenient location for adding an ozonator. The ozone is drawn in, and mixed with the water via the spa jets. All spas have a heating system of some kind, and most are electric. Water is warmed as it passes through a heat exchanger. Occasionally, spas have external heaters, which are usually gas fired.