Lighting, Light Fixtures, Ceiling and Exhaust Fans - medallion

There is a hole the size of my fist in the ceiling where an old fan used to be but it was light and attached poorly to a piece of wood .
I am reading I should get a brace kit but can't picture it-I guess it goes in the hole and somehow uses thhe joists(only can get to from beneath) to hold on. The word medallion keeps coming up when I read this forum for help but I don't understand what it is-can you explain?
Thanx.

A visit to your home center will instantly reveal how a fan brace kit works. It has an expandable bar with prongs on the end that bite into the joists on either side. So you stick the bar up through the hole, set its feet on the drywall with the bar running perpendicular to the joists, and turn it with a wrench until it expands against, and bites into, the joists. Then a "U" bolt goes over the bar and the fan-rated round metal electrical box mounts to the U-bolt.

A medallion is a cosmetic device. It's a decorative round disc of plastic with a hole in the center, and comes in various diameters. It is only necessary if the hole in your ceiling is bigger than what the fan bell housing will cover (which is maybe about a 5-inch-diameter hole). It is used in lieu of patching the hole in the ceiling. Since your hole is only fist shaped, and if your hole is where you want to put up the fan, then you probably won't need a medallion.

Here are some examples of medallions. (http://www.farreys.com/ceiling_fans/westinghouse/fan_medallions.html)

This is what you would be looking for. It fits through the hole for the box and attaches to the joists.

http://www.farreys.com/ceiling_fans/westinghouse/fan_accessories.html

Thank you both for your advice and referrals.
I tried sending a reply with a quote in color but the prompt kept saying my message was too short and needed more than 10 characters; I had many more than that. At least the fan idea is under way. Regards,