On Windows it's: {OS Partition}:/Users/{user name}/Documents/{Euro Truck Simulator 2 or American Truck Simulator 2}/config.cfg
{OS Partition}:/Users/{user name}/Documents/{Euro Truck Simulator 2 or American Truck Simulator 2}/config.cfg
TODO: Linux and mac
The item creation window will appear select the model you want to create (2) in our case it will be simple_cube/simple_cube.pmd.
Place the model into the world by clicking left mouse button and close item creation dialog by clicking on it and clicking Escape button on keyboard.
Change camera to bird camera using C key on keyboard and fly to your box to see it in game.