After completing your first purchase, you can Search for all types of items and browse the Catalogs!
From the website:
Click the menu icon in the upper right of Tophatter and click Search, then enter some keywords to describe what you're looking for.
From the app:
Tap Browse, then tap the magnifying glass icon in the upper right.
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.