Imagine you woke up one morning to find a ton or so of rocks, a pile of sand, and a barrel or two of toxic waste in your driveway. Imagine now that you woke up to find a new truck in your driveway. Sure, it happens every day. Trucks are valuable. Even if you didn't want the truck, you could sell it.
Engineers work to find ways to turn worthless stuff to things of value.
Mechanical engineers design the body, suspension, and drive train. Electrical engineers design the radio, the lights, the cruise control and the computer that controls the engine. Chemical engineers turn gunk into oil, gasoline and plastics. Civil engineers design the roads the trucks travel on. Industrial Engineers are responsible for finding better ways to make and do things.