In order to create models for the SFM Workshop, you will need to compile them from source assets. You can't simply copy them from other games, due to the format differences between games. If you have a copy of Maya, we’ve added the DMX Export Manager script under the Valve menu that will automatically put models, materials and textures into the proper directories for the SFM workshop. If you don’t have Maya, you can create your own .qc file, and compile your model manually. See Exporting a model and Compiling a model for more information. If you run the SFM from Steam, it will automatically create the appropriate model, material and sound directories within the default usermod mod, located here:
Within that mod, your directory structure should look like this:
You can put assets anywhere within those directories, but it's always a good idea to add a parent directory that's named specifically to you, so that your assets don't conflict with another creator's assets. For example, if you’ve recorded your best impression of Dr. Kleiner, (and your name is Jon Smith) you might put those sound files in:
Note that now that assets can be in any directory, you'll want to be careful not to have their names conflict with any existing game assets that ship with the SFM, since the game assets will take precedence. There is a way for users to override player models however - see Overriding Game Models.