Buy a car. It parks itself and earns coins every second, including while you are away.

Drag one car onto another of the same level. They merge into the next model, which earns far more than the two you gave up.

Spend coins on extra bays, and on TUNE, which multiplies everything the lot earns.

Sixteen models per line, seven lines, 112 cars in all. Your lot gets one line and keeps it for as long as your save exists.