PCB Internals
Middle is the substrate (fiberglass, epoxy), that holds stuff together. Thin sheet of copper on each side of the substrate. They then etch the copper to only have the copper etc. Then, a solder mask is placed on top of the board to avoid shorts, protect oxidation. Then an electrolysis emirgen with nickel and gold or whatever is used to protect the rest of the copper
Capacitors
Electricians love capacitors - they act as a mini batter to smooth out voltage fluctuations, and high frequency fluctuations pass easily (ac current passes through with low impedance).
Diode
Zener
This type of diode allows current to flow in the reverse direction when a certain voltage (Zener Voltage) is achieved. So if there is enough “electrical pressure” it can force thru the other way
KiCAD ERC
Input - can read signals
Output - drive signal
Bidirection - read and drive
Power input - input power
Power output - power
Passive - connected however (resistors, capacitors, etc)
Traces / PCBing
use a trace width calculator
avoid vias - but vias can be used
use copper fills