General GPIO Tutorial

GPIO (General-purpose Input/Output) is just a hardware pin that can be used to send or receive a digital signal. It is not meant for high-speed communications, just a simple way to show a state, kind of like an electronics version of bool.

Interrupts are a way to trigger the processor to run certain code when the state of a GPIO pin changes in a desired way. For example, a falling-edge interrupt will trigger code execution when the digital input transitions from high/true to low/false.

Pull-up/-down resistors are resistors that you can connect from the input pin to either Vcc (3.3V) or GND. These are fairly high resistance, usually 10k-100k, and simply act as a way to bias the pin to a certain state if nothing else is acting on it, giving you a reliable default. If a pin is leaft "floating", i.e. disconnected, it is not guaranteed which state will be read, which is undesirable.