Though, not specific but actually:
How to read an electronic schematic?
How to identify its different labels and part?
How to figure if its functional or not?
What is the role of a resistor inside an electronic circuit?
Resistor: as voltage, current limiting, timing etc divider
What is the role of a capacitor inside an electronic circuit?
Capacitor: Filter, ripples rejection, timing etc
What is the role of a inductor inside an electronic circuit?
Inductor: low-pass filter, stores energy in a magnetic field
What is the role of a diode inside an electronic circuit?
Diode: rectification, voltage control, DC anti-reverse protection etc
What is the role of a transistor inside an electronic circuit?
Transistor: Switching, current gain etc
Their uses are almost limitless!