As we know very well by now, it's okay to switch on/off LEDs, and as we are going to see in the next chapter, to switch on/off many things too by using digital pins as output on the Arduino.
We also know how to read states from digital pins set up as inputs, and even values from 0 to 1023 from the analog inputs from in the ADC.
As far as we know, there isn't analog output on the Arduino.
What would an analog output add? It would provide a way to write values other than only 0 and 1, I mean 0 V and 5 V. This would be nice but would require an expensive DAC.
Indeed, there isn't a DAC on Arduino boards.
The pulse-width modulation is a very common technique used to mimic analog output ...