The 2 replies above hit the nail on the Head. What it drives etc can change from engine to engine. If you take an example of the CFM56, The High Pressure Compressor (N2), via gears and a tower shaft, drive the Accessory Gearbox. In turn, items such as the Hydraulic Pump, IDG, HMU, Oil Pump, Fadec Alternator etc are connected directly on the Accessory Gearbox.
In order to start the engine, we have a Starter Motor which is Pneumatically operated. This motor is mounted to the Accessory Gearbox also. Therefore, provided we have sufficient air supply, by opening the Start Air Valve we turn the starter motor...via the tower shaft this then turns the N2 (Hp compressor and Hp turbine). Off hand on a 320 series a/c, the N2 is rotated and at 16% N2 we get ignition, 22% is Fuel flow then engine accelerates to Idle.