Because this course encourage people to use as most protocol as they can, so it has some uneccessary files (libraries & sources).

Sensors files (sensors.h & sensors.cpp) are used to read photoresistors.
Servos files (servos.h & servos.cpp) are used to controll servos.
Process files (process.h & process.cpp) are used to combine function of sensors & servos files to operate system.

RTC files (rtc.h & rtc.cpp) are used to communicate with DS3231 for RTC applications.
TFT files (tft.h & tft.cpp) are used to show on TFT ILI9225 for applications need show information.
Battery files (battery.h & battery.cpp) are used to detect battery for battery applications.