Search Relevance?

To all

I am looking into what it would take to implement a search function that
orders items by relevance. In other words, the highest relevance would
appear on the top of the page.

Currently, I order items by part number and then by alphabetic order in
the description and also order them by how they are ordered in the
database.

First, what sort of data needs to be added to order them by "relevance"

Is this something that's very hard to do? In other words, would I need
the resources available at Amazon or could this be done by a highly
skilled Designer, like myself, doing everything on my own?

What would the logic be?

Thanks for any ideas