Diode (D1)
Diodes allow current to flow one way in a circuit. They are polarized, meaning their orientation matters.
Ensure the side of the diode with the stripe is over the stripe drawn on the PCB.
Bend its leads just like you did for the resistors in the practice kit , insert it into the PCB, then solder.
Clip the leads SAFELY, holding them as you snip. Wear safety glasses!
Component Placement
As a general rule, you will always place a component on the side of the PCB with the silk screen label (i.e., the writing printed on it) for that component.
The designator (e.g., "D1") will usually be printed, as well as an outline or other drawing to provide a visual reference. Place the component on top of this drawing.
WHAT DOES IT DO?
D1: as the signal alternates between positive and negative, this diode changes the way the transistor responds, resulting in asymmetric distortion