i think someone's bored
also use lots of Green connectors at all angles on the bonnet, and anywhere that needs a smooth corner.
make a 2 layer rectangle box for stable construction
add axels and wheels (so that axels can spin but wheels are fixed to axels)
add a motor / rubberband / whatever you want to drive the car
optional - add some coating to the wheels so they are more round and drive easier
add everything else with whatever pieces youd like
Buy or build each of the following:
Wheels, axels, tires, chasis, seat, steering mechanism, motor, mirrors, signal lights, headlamps, seatbelts, and a speedometer.
Brakes, a body, airbags, etc are optional.
It's a big topic, please be moe specific.
Notice that Jack999 has categorized this in Knex. I don't think he means a real car.