This should help. If you're not using MS3D, you'll need some kind of plugin that exports references and animations to .smd files, and a
Half-Life model compiler. (It's not required you use this program, it's just a simple frontend. I can't remember where you get the plain CLI studiomdl, but it comes included with that program.)
The model is then inserted into the map as an
env_model. If you're using Hammer 3.5, you'll see it rendered in-editor.