On the last page of the selling process, you'll have an option to save your auction as a draft instead of listing it now. If you do this, your auction will be saved for you to edit and/or post (or delete) at a later time. To find your saved auctions draft, go to Members' Area > Selling > Drafts. Here you will see a list of your drafts. To edit or post the auction, click the "List Now" link to the right of the auction's title in this list, under the "Options" heading. You will be taken back through the selling process pages, but these pages will be prefilled with the information you entered before you saved the draft. You can make any edits you wish, and when you get to the end of the process, click the "List Now" button.
You can preview the auction from your list of drafts by clicking on the auction's title. To delete the draft, click the link that says "Delete" under the "Options" heading.