Potentially stupid question

[The_Great_Walter]

I'm relatively new to Garry's Mod, and I seem to be experiencing a problem...from what I gather, the CS:S, Mattress Mod(whatever that is) content etc should be accessible for you to toy with in the mod, as it is marked as enabled, but all I see is HL2 models, props, etc...it says if it isn't there you should restart the game and I did so, but still no extra-HL2 features....am I being really dumb by assuming I should have that, or missing something obvious or what? Please enlighten me as to how to solve this...