Hi Robert!
After you select the category, you will see two links below the category box: one that says "Find Product" and another that says "Custom Item Specifics." By clicking on the Custom Item Specifics link, a window will pop open that shows the available Item Specifics for that category.
By clicking your cursor in one of the text boxes, you will see a menu of specifics that you can choose from, or enter your own. There is also a place to enter your own specific if necessary at the top.
Hope that helps, and happy selling!