After logging in you can go to the Market Place and put some ads in. Click on Market in the red banner on top of the page here. In there, on the left side, you will see at the bottom, My Market and the fly out is My Listings and My Market settings. Click the latter to set up your preferences. You will need a Skrill (Money Bookers is the old name) account in order to receive moneys from you sale. 8% is the fee at completion of the sale for you in both Buy it now and in Auction format. For Auction format both you and the buyer pay an 8% fee. This is way cheaper than other sites like eBay where the fees amount to about 20% for the seller. After setting up your preferences you can then list your items in the Sell an Item link just above the My Market and About the Market tabs on the left of the page. Read about the Market there too. There are also Rules you should read up on too.
Hope this helps and if you have any problems, contact me or ask here.