Product tab to show Catebories instead of all products

I got a site and im using a theme. Basically its going to be an online store. i have pruducts that are categorized and basically when i click on my product tab i want my page to show all the categories instead of all the products. also is there a way to to get my products to be more of a grid view than 1 large item then smaller ones below. i am using the Sentient them from woothemes if anyone cares to know. and my website is http://www.woodforcabinets.com . on the navigation menu when you click on corbels i want it to show the categories instead of all the corbels