Looking for information on how does 5 speed fan rotary switch for a ceiling fan increase and decrease the fan speed at any given time.

The multi-speed fans have an electronic switch that varies the voltage reaching the motor. A full 110 vac produces the highest speed, all other speeds are lower voltages.

Some fans have multiple windings and use a multiple pole switch.

Labman is correct, those would be a better quality fans usually in the $175-250.

Actually it's usually the cheaper fans that have motors with multiple taps. Better quality fans usually have single speed motors and use capacitors to create different speeds.

But the OP is asking about wall controls. Most 5 speed controls use a choke, or transformer, to reduce the voltage going to the motor.

Ceiling fan remote controls - help and FAQ- Ceiling Fans N More