When you do something on the internet like watch a movie, check your email, or join a website, different parts of the internet need to talk to each other. This is called propagation of schema. It's like a game of telephone, but instead of one person at a time whispering something, it's computers sending data back and forth. First, your computer (the sender) sends a message through the internet to another computer (the receiver) with instructions on what you would like to do. Then, the receiver computer sends a message back to the sender computer saying whether it could do it or not. Finally, the sender computer knows whether the request was successful or not, and that's how things get done on the internet!