I remember happily going through these each day after school until I could do everything.

There wasn't much on YouTube at the time but I also think YouTube is a worse resource for pretty much all of these simple tricks. All you need is a slow loop to learn any ball juggling trick.

There was also a similar site that let you input siteswaps.

The noob gains once you get comfortable with 3 balls are addictive, compared to later patterns or tricks that can take hours, days or even weeks to pick up.