Video narration
How does your Arduino Uno turn the code you write into an action? Think of a recipe: you write instructions in a form you can read, then they're carried out in order. But the microcontroller doesn't read your sketch like a person. Your sketch is for you; the chip needs instructions in a form it can run. The sketch must compile-be translated into machine instructions the chip can run-before it is uploaded to the Uno. Only then does the microcontroller execute it. At startup, setup() runs once, for the actions that need to happen first. Then loop() repeats, letting the program keep controlling the Uno's pins. So how does your code become action? It is compiled into instructions and uploaded; the microcontroller runs setup() once, then repeats loop() to control its pins as your program directs.