Flow Graphs(ing) explained in full?

[Penney]

Took a look around, Couldn't find anything this time around.

I know a little about flow graphs but I really have no idea how to read them properly and make judgements from them that well. If anyone knows lots about them or knows of a tutorial on them that explains them in full or lots of detail I'd love to see it or hear from them.

Thanks in advance
Keegan

edit: my bad, I ment more specifically how Showbudget works. But I found the dev wiki about it so I think that answeres my own query

http://developer.valvesoftware.com/wiki/Showbudget

but alas it doesnt really explain much other then what things are and represent :S