You need a 12 VDC power supply. If you look on the back of things like cell phone charges, they will usually say something like output 5 VDC 0.5 amps. You need something that says output 12 VDC. Then you need to hook the wires up to the DC portion of your little thermostat. You can usually find something like it at Radio Shack, or you can find an old power supply at a thrift store. Make sure you avoid AC though. I accidentally bought an AC one :-( for my latest project.
You may also need a voltmeter to determine which side is positive and which side is negative, or you might break your thermostat. Harbor freight sells them for like $5 bucks I think.
Be careful not to electrocute yourself, if you don't feel comfortable doing some of the things yourself do more research or get someone with more experience to help you.