I am just getting started working with small electronics. I have soldered together a few kits and recently converted a car stereo into a home stereo. With all of this soldering, I found this schematic for a soldering fan/lamp that is made out of a computer fan and two LEDs.
In the description that goes along with the instructions, they explain that the zener diode allows for the LEDs to receive a fixed voltage. I looked up zener diode and saw that it was a diode that allowed for current to flow in the opposite direction if the voltage was high enough. I am having a hard time understanding how being able to switch the direction of the current fixes the voltage?