There are various combinations to wiring in the mid-range speakers either using the headunit as the source or purchasing a seperate amplifer to power them. The same applies to subwoofers where you can have a single speaker running into an amplifier known as Mono which also powers the speaker differently usually by giving it less OHMs (bridgeable) or running more then 1 subwoofer into a 2CH, 4CH amplifier, etc....
I wont go into all the combinations, nor will i go on about OHMs, Watts, RMS, etc which all come into play but i will post the most common and basic install, which will be using a Headunit, 4 speakers running off of headunit, 1 subwoofer, Amplifier and a Capacitor. The only thing that isnt shown in the pic is the RCA cables which are color coded and a basic pop-on terminal from the headunit to the amplifer direct.
Whenever installing your own soundsystem, always read the instruction manaul for connections being made along with color coding. Always keep wires shielded at all times to prevent the chance of a short which could also cause a fire.
Dual voice coil Subwoofers (DVC)Before deciding on buying a DVC subwoofer, make sure the amplifier you get will handle them. As youll see in the diagrams, the ohms
break down as they enter the amplifier depending on how many DVC subs you have installed.