Metcalfe's law explained.
Imagine you have a new toy that only you have. It's fun to play with, but it's not very valuable.
Now imagine that your best friend gets the same toy. Now you have someone to play with, and the toy is more valuable to both of you because you can play together.
If every kid in your grade gets the toy, it becomes even more valuable because you can play with more people. The more people who have the toy, the more valuable it becomes.
This is what Metcalfe's law says about networks, like the internet or a phone network. The more people who are connected to the network, the more valuable the network becomes.