Just follow these steps:

1. Go to the Search page. You can get there by clicking the Search button at the top of any eBay page.
2. Click the Advanced Search tab.
3. Enter your search keywords and other search options (if desired).
4. Click the "Completed Items" checkbox offered in the section Refine your search.
5. Click the Search button, and you'll get a list of items matching your search that have ended during the last 15 days.