In our first episode about the monumental Goldberg Variations, Christian shows how to break down a canon (round). Unlike "Row, Row, Row Your Boat," the two parts in this canon do not start on the same note. But we can also learn about how this canon was written by using a different perspective entirely. The recipe is simple: start with a very simple melody; add harmony (at the sixth interval), making the melody into two parts; delay one part by a beat (it won't work without this part!), causing some momentary tensions; decorate everything with ornamentation. Because of the delay, you now have a ready-made canon. Now just add a bass line so it complements the rest of the Goldberg music and it's done! You now have three-part music where the top two parts are a canon at the sixth.
That may have been it for the instructions, but there is still artfulness in the execution. The way the leader of the canon predicts the follower is a way for us a glimpse into the immediate future -- this is one of the temporal tricks of music.
Jean Rondeau plays this variation in a performance of the entire work for the Netherlands Bach Society's All of Bach project: https://youtu.be/1AtOPiG5jyk?t=3141