After completing your first purchase, you can Search for all types of items!
From the website:
Click the menu icon in the upper right of Tophatter, then click Search, and enter some keywords to describe what you're looking for. Optionally, click Browse, to view a variety of deals.
From the app:
Tap the menu icon in the upper left, then tap Browse, then tap the magnifying glass icon in the upper right and enter some keywords to describe what you're looking for.
Many items are available to Buy Now, or you can tap the heart icon and set a Reminder, so you don't miss the item when it opens for bids.