Using PHP for file IO

I am dealing mainly with a nested array of objects that I would like to be able to save to a .txt or .html file. Because flash can't do this (I assume for security reasons) I need to use a PHP script. The only problem is, I don't know how.

Can someone please inform me of how to save a flash variable with PHP?

Also, I'd like to know how to get actionscript to read the file in again.

Thanks in advance,
Raphael