To search, you'll need to enter part of the name of whatever you're searching for and then hit enter. A list then comes up with all of the items that have whatever you typed in the name.

In your case, you'll also have to change the parameters from TF2 items to steam items, which is found in a little dropdown next to the place you'd enter the text.

The change was done because it's less taxing on the system than loading all the items at once when people usually have something in mind when searching.