The item browser is very similar to the market browser in the Eve client.
The items are organized into categories, and you can navigate through the categories and sub-categories from a tree-like structure.
Clicking on a category will either expand it to display its sub-categories, or if it's a terminal leaf, it will display the list of items in the table on the right.
The organization is a little different than in the Eve client. It has been slightly altered to make it easier to find an item, and to accommodate for the extra categories (like Clones or Outposts).