Sources
These are the sources I used in writing this section of the guide as well as additional resources for you to learn more about control theory.
https://en.wikipedia.org/wiki/Control_theory
https://stuypulse.com/resources/
https://www.youtube.com/watch?v=lBC1nEq0_nk
https://file.tavsys.net/control/controls-engineering-in-frc.pdf
https://docs.wpilib.org/en/stable/docs/software/advanced-controls/controllers/index.html