What is the resistor's role in a circuit?
to reduce the flow of electricity.
About the NPN Transistor
If the flat side is facing you then the left prong of the NPN transistor emits electricity. If the middle or base prong is powered it can turn on lights, make buzzers buzz, and any other things that are connected to the left prong. And the right prong is the collector.
Introducing The Potentiometer
The right and left prong have a wire connecting them. the middle wire has a wire that moves from one side of the connecting wire to the other (when turning the knob). More electricity or less electricity goes through depending on where the knob is turned.
How is the IR LED unplugged?
It is unplugged by disconnecting the resistor that is connected to the IR LED.
Capacitor leaks current as it charges
The light goes out because when the capacitor is full, then current cannot flow through it so no current goes to the LED.
About the PNP Circuit
The PNP Circuit is the opposite of the NPN Circuit.