I can only explain how the program works. It works like any other product I have seen that utilizes these little mini search boxes. There is no search by username feature on those mini quick search boxes.
1. If you are on the home page then anything you enter on that mini box will search all category photos title and description extra fields etc for the search word.
2. If you are within a category the search box will do the same thing as the home page only limiting the search results to the category you are in.
3. The search by username feature is located on the main search page