The grey bar magnet

The grey bar magnet (1) creates a magnetic field round itself.
ii. The magnetic field lines (2) expands imperceptibly upward through the metal guitar strings that are situated over the pickup.
iii. The brown Guitar string (3) close to the gains magnetism by the magnetic field. When the string is strummed or plucked (vibrates), it creates its own magnetic field.
iv. The yellow coil wire (4) that is wrapped over the pickup, senses this magnetic field. A minor electric current is created in the coil due to the magnetic field.
v. The amplifier (5) boost the low input signal so as to make it powerful enough to drive a loudspeaker.
vi. The loudspeaker (6) changes the current into sound that we can listen to and enjoy.