define THIS_SCRIPT and Path question

[Dankinit]

I have two basic questions, and sorry if this has been covered. I'm writing some hacks for vb3:

1. How do i define the path at the top of the navbar? For instance it has:
" vBulletin.org Forum > General Codings/Questions > PHP / MySQL / JS / " at the top of this page, how would I do this for my custom page?

2. Not sure if this is related to question #1, what does this part do exactly? I understand this is used throughout on many scripts at the top, but where/how does this information get used?

PHP Code:

define('THIS_SCRIPT', 'profile'); 


Thanks for any help!