It's a protocol that allows users from different apps to communicate. Instead of signing up with an email and password you generate a key pair, the private key acts like a password.
That's really all a new user needs to know, they can learn everything else once they're here.

I like to compare it to driving a car, you don't need advanced knowledge of the mechanical components and how everything functions to drive the car.
you can learn to drive first, then learn how it actually works later on.