first time system, volkswagen rabbit

You didn't list the year but look under the drivers side dash at the fuse panel. Some VW's have large gauge terminals there and the current rating will be printed there as well. I think the largest is 30a so if you are exceeding that much current (you didn't supply that info either) you must go directly to the battery, which is always reccomended with amplifiers anyhow.

No real "directions" to do that..it comes with experience but on those vehicles there should be a factory grommet (a round rubber seal) near the battry location at the firewall. If you can't find it I know there is at least one by the drivers side firewall. somethines you can use the hood release cable grommet as well...carefully make a small slit in the rubber with a razor knife and push the wire through.

In certain vehicles is may be easier to drill your own hole..especially if using large ga. wire. The rules for that are DO NOT DRILL unless you know whats on the other side and use a grommet so the metal edges do not cut into the insulation. Always Use a fuse as close as possible to the battery to prevent fires and keep the wire away from heat (like exhaust manufolds and turbos) and moving parts such as steering knuckles etc.by using wire ties..cover the wire with some split loom for a pro finish.

Good Luck with it.