Walmart has a comprehensive catalog that can be easily accessed online via http://www.walmart.com/cp/All-Departments/121828. Every department in the store listed on the page. A specific item search tool is featured at the very top of the page beside the "Walmart" logo.
Each department's listing has a "+" beside it. Click on this icon to display a more comprehensive listing of sub-categories within each department. If you are searching for a particular item, enter the item's name in the search box at the top of the page. Many of Walmart's online products are available for in-store pickup; if this option is available, you will be notified when you place an order for that product.