Cranks are normally hand-operated. It is important to note that operating a crank can rapidly become tiring. For many applications pedal power (which uses the larger leg muscles) may be a better option.
Hand-cranks are still often a good choice for small-scale mechanical grinders (e.g. coffee grinder), millers, rollers (e.g. pasta machine), shellers, and the like.
Some small-scale water pumps are also hand-cranked.
Hand cranked and (foot powered) electoronic machinery is making a small come back.
The word "crank" is also used for mechanical linkages that convert reciprocating linear motion into rotary motion or vice-versa.