Hi everyone

I'm trying to get a handle on Cycles materials and thought that if I could use some of the many materials folk share, I could dissect and get a better understanding.  I would really appreciate it if someone would be kind enough to explain in layman's terms how I go about saving from the downloads, what file structure is needed, if there is anywhere special to keep them and how to go about getting them onto a surface in Blender.

Any particular download sites recommended?

Thank you in anticipation :)