Since you are a Gold level member here then the section to list your domains for sale is the section titled "Domains for sale under $250". Those are for domains with a price of under $250. I believe you must have a price listed, as well as the usual information such as the domains expiration date, it's registrar and form of payment you accept. Make sure you read the site's rules pertaining to domain sales before posting any, just to make sure you have everything it requires.
If you want to sell domains with a price higher than that you will need to upgrade your membership to a higher level.