Put categories on top nav bar

I can see how to customize the sidebars, but how can I move something, such as the categories to the top nav bar? I am going to have maybe 3 or 4 main categories of items i will be selling with multiple subcategories under each. How can I just list the 3 or 4 main categories on the top? I will be having someone build me a custom template for this eventually but want to get the store set up first.

There is a default ul list that can be displayed in the header in it's own div

admin > config > layout settings > cat tabs > on