They are a brushless motor plus controller all on one unit. Some are controllable, some aren't, but they usually run fine from 7V upto about 15V, speed proportional to voltage - although this is a convenient way to control usually. Controllable speed ones have a pin to control them, many have a sense pin that is used on a motherboard by the bios to detect if the fan bearings have siezed up.
Simple on-off control (not PWM) is just a transistor I think (perhaps a protection diode too?)