If you refer to a multi channel account you can create a new product after logging in to your account by selecting My Product Catalog from the Products menu and then clicking on the Add New Product button. Alternately, you can click directly on the Listings tab and on the page that follows select either Amazon or eBay and then click on the Add listing button for the channel you are creating a listing for.
If you refer to an eBay only account you need only hover over the listings menu, and then select Create New from that menu to reach the one page lister. Note that the menu headings differ depending on whether or not you are using the multi channel product - for an eBay only account you will have the menu headings for Listings, Images, Gallery, Profiles etc., while in a Multi Channel account you would see only Products, Listings and Sales as the other menus are available from icons near the top of the page. (I took a look and the account associated with your email address is an eBay only account.)
If you have further questions or run into difficulty, please feel free to file a support case from under the Help tab of the site or use the support icon in the lower right of the site pages.