Agreed with @Adirondackwannabe that Little League and Pony would usually welcome additional scorekeepers…do any of your friends have kids who participate? You could ask to get involved with their teams. Most kids leagues will fire up practices/games in the March timeframe. When I was first learning, I sat with someone who knew the process, and that was super helpful to get the hang of it.
You could watch baseball on TV and practice. And, as much as I enjoy the old-fashioned paper & pencil, the world is changing so I feel compelled to mention two excellent baseball scoring apps – GameChanger and iScore. My personal preference is GameChanger, which I have used for several years now…the apps give you the advantage of quickly clicking around the screen to describe the action, allow you to easily manage the lineups, broadcast games over the internet to family and fans who can’t attend, AND, best of all, calculate stats for you. Both apps can be used on a phone or tablet at games, and I’m pretty sure they both have training modes, so you could do some practice.
Good luck!