I only got FFT after following the course `Introduction to Graduate Algorithms`( Georgia Tech) and implementing everything from the lectures in python. It is really good course:
Your link just asks me for a login, which of course I don’t have. I’ve not heard of Ed before. I am interested but the “see how it works” section doesn’t really tell you how it works. As is the trend, it seems you have to sign up first. Shame.