the forever make the code run if I press the button again the if is used to detect input of the button A so when I press it waits 500ms then displays the corresponding led combination then waits 500ms again then the next combination and so on

The (on shake) function takes input from the accelerometer about the movement of the micro: bit and runs the code inside the block (on shake) which is in this case the blocks (show number) and (pick a random number from [] to []) we put from [1] to [6] as a typical dice that was the code which is processed when the accelerometer on the micro: bit registers movement then it outputs the code on the display