Phase 0: #1

Decided that I need to understand things to really make a worthwhile custom board. So I devised a learning plan with the help of AI. The knowledge gained here would carry forward into my future hardware projects.

phase 0 starts with knowing what I am working with and its functioning.
Today I learnt about GPIO and about its input and output high and low. Then can floating inputs and how pull up and pull down resistors help keep it fixed.
However I do not quite get the secondary functions like ADC, I^2C, SPI and UART.
Though matrix switching feels like a really smart move to convert dependence from n^2 to n for amount of pins required.
Then came diodes and ghosting which I did not quite get.

If anyone has read this far, it’s a request could you please clear this doubt of mine.
I want to be more clear about the ghosting and matrix scanning part: matrix scanning works in cycles. The firmware first pulls the row pin to 0 and checks which of the column pins are 0. if the output (row pin) and input (column pin) are both at 0V what part does current play in reading as ghosting is explained as current flows backwards by finding an alternate pathway. If to read both are at 0 potential so no current should flow between them then how does it give a false reading when backward current flows.
and Thank you for your help in advance.

tomorrow I hope to be looking at quadrature encoders, schematic, footprint, net, trace, via , ERC, DRC and gerber and after that I at least hope I know what part (leds, switches, rotary encoders and oled) goes into which pin. wish me the best!!!! Ganbare