Knowing means to understand something or to have information about it. It's like when you learn that the sky is blue or that 2 + 2 equals 4. When you know these things, you can remember them and use that information in different ways.
For example, if you know how to tie your shoes, that means you’ve learned how to do it, and you can do it again whenever you want. Knowing can help you with your schoolwork, playing games, and even talking to your friends.
So, when we say 'I know,' it means we have learned something and now we understand it well enough to remember and use it!