Change Category Display

[Mookie_Jam]

I would like to change how the items are shown inside a category. In stead of appearing as a list, I would like them to appear, for instance, in a table of 3 colums appearinf the product info in each cell, with also a little border in shape of containing box.

 

How can I do it? What files I have to change?

 

Thanks for your help!