Help Gmod and counterstrike

Very sorry for asking what must be a simple question to you all but its for my handicapped son that plays your game and he loves it .
He has seen on utube the counterstrike figures incorporated with Gmod. If he downloads counterstrike through steam or buy the PC game can he very simply combine the 2 so he can use figures from the game on Gmod?
If no how can he or is there not a simple way of getting counterstike figures onto the Gmod game?

If you buy Counter-Strike: Source, the figures (ragdolls), props (models), weapons, and maps will be able to play with Gmod.

If you buy Counter-Strike 1.6 (the non-source version), it will not work, because Gmod and CS 1.6 are on different engines.

Is this Counter-strike source released Nov 2004 £13.99 on steam?

Can he also do the same with Left-4 dead that has the steam-play symbol?

Will these extra items show up automaticly in Gmod?

Thankyou very much for your help he will be over the moon when he finds out he can actually combine the 2.

Left 4 Dead won’t work with Garry’s Mod but Counter-Strike: Source will.

L4D can be used on GMod, but GM_Mount2 by aVoN is needed