You have to compile the model to get it ingame. Depending on if you want it in HL1 or HL2, it'll be a little different. I'm guessing you want it in HL2, so I can't help you there. Tutorials can, though.
What exactly does the back of the box say? It's too low-quality to read it. The front of the box looks kinda low-quality too. Did you do it like that on purpose? It's just a box with a texture applied to it, so the texture should look good.
Garry's Mod owns. =)