On the create listing page, you should see a yellowish bar toward the top, above the description box. It has two choices in it -- one for auction and another for fixed price. Choose Fixed Price. Make sure you fill out the Buy It Now/Fixed Price pricing box for the cost of your item and leave the Starting Bid price at 0. I hope this helps.
You would fill out the section for fixed price in inventory, in the Auction Information tab. When you select your inventory item and you click on Launch, on the next page, you'll need to choose the venue to list your item. There is a selection there for eBay Fixed Price so just be sure that you pick that option.
