sorry if this is a stupid question :(

if i get garrys mod will i be able to use all the HL2 weapons, or do i need to actually have the game? could i use the demo if i cant?

Yes.
You can still use all of the HL2 weapons if you have CS:S + Garry’s Mod.

yes you will, remember that to run gmod you need a source game, eg. hl2, Cs:s, TF2, DoD:S HL2:Dm
i would reccomend Cs:s (most weapons and textures have some cs:s element)

[editline]08:09PM[/editline]

After finishing typing i noticed the above user beat me to it…

Yes, comrade. In fact, you spawn with the shotgun, rpg, grenade, crossbow, ar2, grav gun and all the others. Plus, a tool gun, camera, and phys gun (a souped up grav gun)