You get two ballasts, which convert energy from your 12V battery to whatever voltage needed to light the HID bulbs. The bulb comes with wires attached to it already, and so does the ballast. The ballast has one open slot though. In that slot, goes the only wire that can fit in the ballast, straight from the bulb. Now the tricky part is, there should be two rectangle looking wires, pos and neg. You need to connect those to the pos and neg outlet of the original headlight. If it ends up being "plug-n-play" like it should, it'll fit right into the two slots. If it doesn't, like for me, you'll have to do some splicing.
In order to not ruin my HID Kit and my factory harness, I just got a wire extension and connecting it to my harness and my HID kit, so that I don't have to completely splice any of the wires. It should be plug n play if your headlights are completely stock. Mines were aftermarket, so I think that may have caused the problem for me.