Layouts/Pag Design

I am trying to develop a simple shopping cart application using ROR. I
have a categories controller and a products controller, which work fine.
My problem is that I can’t figure out how to get the page to display in
the way that I want. I would like to have the categories list to show
on the left side of the page…it will serve as the site navigation
(navigation thru the product categories). When a category is clicked I
need to display a list of all products in the category on the right side
of the screen. I have not been able to find a clear example on how to
accomplish something like this. Explanations or links to tutorials
would be greatly appreciated. Thanks.