Nano is connected in a basic DC circuit: for 3V it is connected to the third plug on its board.
(Because it was initially connected to the second plug, there was no voltage.)
Lighting up one LED, the resistor was needed so as not to burn out the LED- some LEDs could handle the higher voltage better than others. This was dependent on the color of the LED. The ones that couldn’t blew up.
Although we followed the diagram, LEDs did not light up. LEDs were working when tested individually. The problem was that there was not enough voltage for 2 LEDs, had to connect them in parallel.
In parallel circuits, LEDs share the voltage (both LEDs measured 1.81 volts). We connected two and three LEDs in parallel so there was enough voltage to light the lightbulb. In the picture above, the red LED is brighter because it takes most of the voltage in the circuit because of the order in which the current flows.
https://drive.google.com/file/d/1DWGS6Pftt_SwfgI2NctmUbZe1yimb-Fg/view?usp=sharing
https://drive.google.com/file/d/1DWGS6Pftt_SwfgI2NctmUbZe1yimb-Fg/view
When using the Potentiometer, the circuit follows the path of least resistance to the ground: changing resistance is why LED may not light up.