Regardless of scale, most model trains run from a controlled 12v DC power source with two systems in use. Analogue 12v DC control varies the voltage to the track to control the speed of locomotives on the track. Simple to use on basic layouts, each control knob can control a separate track or circuit.
Digital control (DCC) provides a constant power supply to the track but each locomotive must then contain a DCC micro chip that allows it to be individually controlled from the control panel. The advantage is that realistic effects such as engine noise can be initiated and multiple trains can operate independently on the same section of track.

Lights, points and signals usually require a separate uncontrolled output.