50' roll of 12ga. speaker wire, or 35' if you think you'll need less. You can get it at Wal-Mart, they're pretty cheap and have decent wire.
Remove the battery negative cable!
Open the cover of the crossover, there should be 6 screw posts. they should be marked as follows(yours might be slightly different): IN+, IN-, W+,W-,T+, and T-.. Obviously the IN+ & IN- come from the Amp.
Run a line of 12ga. from the Amp speaker + to the crossover IN+, and do the same for the negative side.
Run a line of 12ga. from the crossover W+ to the 6"(or whatever size comp speaker you have) positive post. Do the same for the negative side.
Run a line of 12ga. from the crossover T+ to the tweeter positive post(or solder the wires together). Do the same for the Negative side.
Done!