One stop shop for yum and information about yum.
The yum HOWTO (probably still somewhat incomplete).
This article. (Self-referentiality! That's a neat trick...)
Duke University Linux User's Group, host to several public mirrors and useful resources.
Current host of the yum website, among other things.
The name says it all. The place to go if you don't understand any tool referenced in this article, or to learn how to set up e.g. a web server or ftp server or network file server.