To crank is to turn or rotate something using a handle or lever. The earliest automobiles required drivers to crank the engine before they could climb in and start driving.
You might crank a paper towel machine in a restroom to unspool the towels, or crank a music box to start it up — in either case, you're turning a handle, which is also called a crank. You can also say that you crank up the engine when you start your car, even though you're not literally turning or winding anything. A completely different kind of crank is a grouchy, opinionated person. This last meaning comes from cranky.