Categories are displayed in all capital letters (GARAGE SALES, LEGALS, etc.). Classifications are upper/lowercase (Auctions, Lost & Found, etc.). You select a category or classification by clicking on it in the box. You may select more than one by holding down the control key while clicking the category or classification header. Short cut: You may select all classifications in any category by selecting the category only. You do not need to select the category and all the classifications within it. Of course that means that if you select a category, you will be searching all classifications within that category, regardless of any individual classifications you select within that category.