Random posts on the main page

Hi,
I’m wondering if anyone can help me. I only started to learn php recently, so basicly i know nothing. However i really need a plugin or a hack that a) randomly shows posts on the main page, b) works with current theme and c) has a step-by-step tutorial for noobs. Can you help me? I googled it and found a couple, but i have no idea how to use them. They provide a function something like “random_posts()” and nothing looking like an rtfm or readme. I have no idea how to use it…

Huge thanks in advance,
pxd.