I wrote a few tutorials about Hints and Leaks, but couldn't find a balance between too simple and really difficult.
There are however a couple of tutorials already on the web, and I asked Eiger if I could post a link.... He agreed.
Try Hints for Hint brush stuff,
LEAKS in Hammer for Hammer LEAK finding or,
LEAKS in Half-Life for finding LEAKS in game.
I will add these to the Glossary today. So there is no need to add pointless spamming to this post, although I am sure that some immature loser will.