A public private key pair is like a secret code or password. It is usually used to keep information safe and secure from everyone except the people that know the code.
Think of it like a lockbox. Inside the lockbox, you can keep important things like money or secrets. To open the lockbox you need a special code or key. That key is like a private key. The private key is like a secret code that only you know.
But other people do need to be able to get information into the lockbox. So you have a public key - this is like a special code that other people can use to give you information, but they can't get into the lockbox themselves.
The public private key pair is a way to make sure only the people with the private key can access the information. It helps to keep your information secure.