Use File->Append from the character.blend and choose the car.blend and then via the Append screen select all the things from the car scene you want to have appended (added) to the character scene…
So I was pretty much trying to do this exact same thing, except that I have tried this and it doesn’t work for me… I don’t know why, but I am really frustrated with Blender… it’s the least user friendly program I have tried to learn!!!
Calm down - Blender’s a large and complex program, and while it’s fun, learning it will take time. To link objects, you go to the File menu, select Link, select the blend file that you want to import, and then select the resource and object that you want to import. What exactly is the problem you’re having?