How would I go about creating a custom search by cloning the default search on wp?

I'm using Gridmarket on a small computer repair/sales site and we are wanting to build a search for printer inks. When I use the default search I get crazy results. I am thinking to clone the default search and use -/+ categories to refine it. I am at a loss for finding the correct function etc; I would need to clone and modify, if you can help it would be much apprecitated.

John