From memory, it comes on in response to pressure in the AC system. On a hot day, it will probably be on most of the time the A/C is on and the car is not moving. More than you probably want to know here.
Yes, it will come on if the coolant temp rises above a set point, around 105C, IIRC.
The mechanical fan. At normal temperatures the fan is driven at less than engine speed by the viscous fluid in the clutch. When the temperature of the air coming off the radiator reaches the fan's set point, the clutch "locks up" and the fan is driven at engine speed, up to a certain point, above which the fan maintains a relatively constant speed.
It is between the fan itself and the drive pulley. #10 in the diagram,