Regardless of scale, most model trains run from a controlled 12v DC power source. Two systems of control are now in widespread use.
DC control varies the voltage on the track, controlling the speed of all the trains on the track. Simple to use on basic layouts, each control knob controls a separate track or circuit.
DCC Digital control uses a uniquely addressed microprocessor (a signal decoder) on board each locomotive or train. This controls the train in response to the instructions it receives from the DCC controller. Each train to be controlled independently and one controller can run several trains on one or multiple tracks.

Lights and colour-light signals require a separate uncontrolled output, usually at 16volts AC. On/Off switches allow control of lighting circuits, while a changeover or On/On switch changes your signals from red to green.
Points can be motorised, allowing remote operation using a passing contact switch to change the route. A Capacitor Discharge Unit (CDU) can help provide positive operation, especially over the longer cable runs encountered as your layout grows. DCC systems offer an alternative, an accessory or point decoder connected to the track and responding to commands from the DCC controller. Several point motors or signals can be connected, reducing the wiring required.