First, watch the video.
Then, practice juggling (re-watch the video as needed).
Finally, juggle as often as possible. It’s like learning to speak a language or getting better at playing a game (chess, for example). The more you do it, the better you (or at least most people) will get at it. What I don’t say in the video is that after awhile you’ll find that juggling is meditative. While at first it’s frustrating, over time it becomes calming. Enjoy!