I learned myself juggling out of boredom when I was kid. Just tennis balls or similar stuff I found. In early 90s, no info anywhere, just started.

2 balls with 2 hands, 2 balls with 1 hand and finally 3 with 2 hands. Didnt push it further, we had too low ceiling for bigger throws that 4 balls would require, and juggling 2 balls in each hand was... tricky to keep up for longer.

Consistency of the toss is exactly how I could keep up, if 1 went off I lost it usually within few throws. Unless I did it on purpose. Recently showed it to my kids, obviously rusty but still had the moves.

Damn, I had so much free time as a kid its surreal now.