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.