Basically you just go to craigslist.com, find your city (or the city closest to you), create a login, and then post your item under the appropriate category. And then there's the fun of waiting for dozens and dozens of responses from people who are really excited to get whatever it is you're trying to get rid of. Like in October when we listed our old fridge and within 24 hours I had received over 50 responses from people wanting it. Ridiculous!
And, it's a great resource for finding quality, used items. We've bought a jogging stroller, a bookcase, a booster seat, and many more. With no bidding, no shipping costs, being able to quickly and easily talk to the seller (and barter for the cost), it's a great place to look for all sorts of things. So take a look - you might find a really good deal!