How to run javascript script only once

Hi all.

I need some help from the experts here. My knowledge of javascript is 0. So here is what I need for my website. I have a script that is a sequencial tooltips, so, for example I can make a tour to my website using javascript. (just like facebook does when they have some new features).
Now I just need to my script only run once when a user enters my url. It is not correct if a user goes to contact me page, then again to homepage and have the script messing around again.

So how can I achieve that?

Thanks very much.