It's incredibly easy to sell on Amazon. If you type in the name of your book/DVD/whatever into the search bar, once it brings up the product page, a box on the right asks if you have one to sell. Click on that box, look at the used prices and determine if its worthwhile. If it is, all you have to do is click fill in your condition information and set your price.
For items listed without a Store account, Amazon takes a 15% commission plus 99 cents per item. You get the remainder plus about $2.99 for shipping (media mail shipping is usually costs you less than that). If you find you are going to sell more than 40 items per month you might want a store account -- they occasionally offer a couple of months free.
Every 2 weeks (or on your request) your earnings are swept into your bank account (you need to provide them the account number). You can also choose to have your earnings disbursed in the form of an Amazon Gift Card. You can accumulate up to $200 on a card in a 6-month period.
For more info on selling on Amazon, check out this eHow <a href="http://www.ehow.com/how_4498575_buy-used-books-resale-amazon.html"target="_blank>article</a>