Okay kiddo, so imagine that you live in a neighborhood where everyone celebrates their birthdays on a different day. Your friend's birthday is on a different day than yours, and so is your teacher's and your neighbor's.
Now, let's say that you have a special toy that you love to play with, but each time you play with it, you need to ask permission from your parents or someone in charge. This is just like how Jewish people need permission to do certain things during a special time called Yom Tov.
Yom Tov is a very important day for Jewish people, like a birthday or a big holiday. But there's a rule that says it's not okay to do certain things on those days. It's just like how you might not be allowed to play with your toy during school time.
But what if your friend's birthday is on a day when you're not allowed to play with your toy? That would be a bummer! So, Jewish people came up with a way to make sure nobody misses out on Yom Tov even if they can't celebrate it on the exact same day as everyone else. They decided that there would be a second day of Yom Tov called "Yom Tov Sheni Shel Galuyot."
This second day means that everyone who couldn't celebrate Yom Tov on the regular day (because it was on a different day for them) can celebrate it on the second day. Just like how you might be allowed to play with your toy on the weekend even if you couldn't play with it during the school week.
It might seem a little bit confusing at first, but the important thing to remember is that Jewish people want everyone to be able to celebrate Yom Tov, and the second day gives even more people a chance to join in the fun!