Do a Google search for those entities. There's a lot of explanations about them. In fact, there's quite some HL2 tutorials out already.
Sites like editlife.net, thewavelength.net, halfwit-2.com, interlopers.net, gamedesign.net, gamewag.com and snarkpit.net all have at least some tutorials. Some are full of it...
EDIT: And hey, don't forget the Source SDK example maps...