Crank has several meanings:

1. A handle that you turn in circles to make something work. Old cars needed a crank to start their engines before electric starters were invented. You might turn a crank to raise a bucket from a well, or use one on a pencil sharpener to make the blade spin. The crank converts your circular motion into the machine's work.
2. To start or operate something by turning. You crank an old-fashioned ice cream maker to freeze the mixture inside. When you crank up music, you're turning it louder (even though modern volume controls don't actually turn anymore). Crank out means to produce something steadily, like when a factory cranks out thousands of toys before the holidays.
3. A grumpy, complaining person. When your neighbor is always cranky about noise or kids playing nearby, people might call them an old crank.

Whether you're cranking a handle, cranking up your effort on a project, or dealing with someone's cranky mood, there's something stubborn and persistent about it.