The basics of an oscillating fan is that it converts the rotary rotation of the fan into a oscillating motion so that the side to side motion of the fan head can be obtained.
Because of the gear ratios, the RPM of the fan is reduced by 160, (Gear ratio of 160:1), and this output will drive the 4 bar mechanism.
The reduced motion output acts at the input for a double rocker 4 bar mechanism which allows the fan head to oscillate side to side.