That means it relies on an amplifier built into the receiver. Any decent receiver won't have this. You'll have to either add an amplifier or get a halfway decent sub with a built-in amp. I highly recommend the Polk PSW-10 for a low-cost sub. I have two of them in a 7.2 setup, and they're wonderful.
If you don't want to spend any more money, you can always go the ghetto route and put an old stereo or something between the pre-out and the subwoofer. Just run a standard RCA cable from the receiver output to the left (or right) CD/tape deck/8 track/whatever input on the stereo, then plug the subwoofer into the left (or right, but keep it the same side as before) speaker output. If the output is RCA, you can cut up an old cable and use it as an adapter. The outer wire is the ground. This will definitely decrease audio quality, but if you're using a cheap non-powered sub, I doubt you'll really notice.
is an explanation of what the "presence" outputs are for. Don't plug the sub into them.
As far as wire ratings, you don't need to worry about them on any reasonable home setup. The only time it really matters is when it's an extremely high-powered system for like a movie theater or concert hall or something.