@scott4 - Yeah it’s just what hole is your home base (the place of greatest resolution, aka the “key” of the song, as explained here:
You can download a positions chart, or look at the circle of 5ths in which case moving 1 space clockwise from key of the harp is your next position. So on a C harmonica, playing in key of F is 12th position, which is -2" and -6 are your root notes.
It just so happens, according to many comments I’ve gotten on the Amazing Grace video, that 12th position turns out to be the easiest place for beginners to play that song. Kinda crazy, but different songs just layout hard or easy in different positions.
It’s a bit of a mind-bender. It’s normal to be confused by positions at the beginning! For anyone doing the Beginner to Boss course, this post may be helpful: