If you want to create a vehicle, check this: http://wiki.beamng.com/Introduction_to_Vehicle_Creation Also you should try NBEditor located in program files (x86)/steam/steamapps/common/beamng.drive/utils/editor/
Well depends on what you want to create. There are a few tools to use. But as posted above you should check this link to see all your answers: http://wiki.beamng.com/Portal It's a link to the beamng wiki and there they explain everything about modding for you and what to use and so on. Even explaining how to make different mods. (everything modding related is under the modding section and the documentation section.)