A private community is kind of like having a special club that only certain people are allowed to join. Imagine you have a treehouse with a sign that says "Members Only." This means that only you and your friends who are part of your club can go inside and have fun together.
A private community works in a similar way, except instead of a treehouse, it might be a group of people who are interested in the same things, like a group of people who like to play soccer or people who enjoy knitting. These people might decide to create a private community so that they can talk and share ideas with each other without other people who aren't interested in soccer or knitting getting in the way.
Just like your treehouse, a private community has rules and might require you to be invited or approved by the people who are already members. This is to make sure that everyone who joins is respectful and interested in the same things as the rest of the group.
Being part of a private community can be really fun because it means that you get to hang out with people who share your interests and passions. But it also means that you have to follow the rules and be a good member so that everyone can have a good time together.