How do I randomize a sequence of squares as such?

Hi, I am looking to code my game as if a 3x3 board of squares randomly flash one at a time until a button is pressed, then stopping the random flashing and selecting one of the squares.

Check out the video beginning at 4:27 for a reference as to what I am referring to.

https://youtu.be/o0RlmLuMP_s?t=267

Thanks.

- Chris

I will do that! Thank you so much LionZ! :-)

- Chris