[eluser]TheFuzzy0ne[/eluser]
Have you read the [url="http://ellislab.com/codeigniter/user-guide/database/index.html"]user guide[/url]? I'm not sure you have, since there is adequate information provided there you get you going.
I don't really understand what you mean by "associate two table fields". If you can post some code that demonstrates that you have read and understood the user guide, I'm sure it will be much easier for someone to help you.