I put in a car model to show up in game and it doesn't appear when I spawn in? Any ideas?

It could be because it is missing a GDT file for the model. I have had to do this for several models, car models included. When you compile, it will say something like missing GDT for asset xmodel NAME_OF_MODEL

1. Open up APE, its the monkey next to Radiant.
2. Create a new GDT by going to file, new GDT. Call it what you want, this will be where all your custom models/textures go, so like "my custom models" or something
3. Create a new asset, by going to file, new asset. Call it the name of the model, you can find out the name either through radiant, or the error that launcher gives you.
4. Put the asset type as xmodel.
5. Put the GDT file as the GDT file you created a few minutes ago.
6. Click OK
7. Now go to file, save all.

And now it should work.