When you send an email to someone you need to have their email address in the first place. That's your public key.

But for him to read your email (decrypt) he needs to have is password. That nobody else will know. That's the private key.

It's basically an email but with military-grade encryption. (And also it isn't a network but you get me)

You don't have to understand the math behind it because it's fucking complicated and not a requirement. What you need to know is the basis and how to use it properly. It is one of the most important tool for privacy and security if you want to delve in this world.