Connecting to a 12v Power Supply
12 volts come from a battery or from a mains adapter.
The battery may be charged from the mains, a vehicle's alternator, solar panels or a wind turbine.
If you want to know more about 12v batteries, you should visit here.
12v Mains Adapter Power Socket How to fit a Power Socket
If you are using a mains powered 12v adapter then you can either cut the small plug off at the end of the adapter wire and 'bodge' your own connection or you can get hold of a socket to plug the adapter into.
Connector Block Terminal Block
With the Power Plug Socket...
See Fitting a Power Socket for more detail... or...
Bodge the Adapter...
Cut the plug off the end of the wire furthest from the body of the adapter, to give yourself as much spare wire to play with as possible. But its always sensible to leave 10cm of wire connected to the plug in case you want to use it later.
If you are Connecting to 12 Volts...
Your options will most likely be...
Soldering or using terminal blocks to connect to wiring that already exists (you should be familiar with the electrics you are going to use);
The Car Plug is the most elegant and you can see how to wire it up here.
Solder your wires direct to Mini-Croc Clips or screw your wires to Big Croc Clips.
Big Crocs Mini Crocs Car Plug How to fit a Car Plug