Finding what's in memory?

[EvilMC]

I've noticed in some scripts, people begin by assigning all sorts of memory locations to variables. It will be something like:

$hitpoints=0x000096BF

That's just a 100% random 'example.' It wasn't taken out of a script.

My question is this:

How do programmers and scripters find out what's where in memory?

Thanks,

Evil Master Chief