Okay kiddo, so think of your brain like a big bookshelf with lots of different books on it. Each book is a different thing that you learn, like how to ride a bike or what the capital of your state is.
Now, when you first learn something new, it's like adding a new book to your brain's bookshelf. But just like with a real bookshelf, if you just put a book on it and don't look at it again, you might forget what's in it.
That's where memory and retention come in. When your brain wants to remember something for a long time, it's like taking that book off the shelf and reading it over and over again until you really get it. The more you read it, the stronger the memory gets and the easier it is to remember it later.
But sometimes it's hard to remember all of the different things you learn, especially if they're not very exciting or interesting. So your brain has ways of prioritizing what's important and what's not. It's like having a special place on your bookshelf for your favorite books - your brain gives more attention and focus to the things that are really important or that you really enjoy learning about.
So if you want to remember something for a long time, you have to keep looking at that "book" in your brain by practicing and reviewing it regularly. And if you want your brain to really focus on something, try to make it as fun and interesting as possible, like adding pictures or stories to help you remember.