You can't choose to list it as an auction when there's no valid offers to the domain in question. Once someone makes his offer you get to choose whether or not you want to take it to auction. Here's the sedo link:
http://sedo.com/auction/overview/
They don't charge you for the auction, but they take at least 10% of the final sale price for all sales
I think this thread should be moved to the "Beginners and Newbies" section or to the "Sedo" section. Any question you might have that is very basic is best asked in the "Beginners and Newbies" section.
You need to upgrade to at least the platinum membership to be able to list your auction here. Good luck.