How the internet fits together

Networks agreeing to carry each other's traffic.

A network of networks

The internet is thousands of independent networks that agree to pass traffic between them. There is no centre and no single owner, which is why it survives large failures.

Your ISP connects you to that mesh and buys transit from larger networks.
Undersea cables carry almost all intercontinental traffic; satellites carry very little.

Standards

It works because everyone implements the same published protocols. The documents are free to read, which is unusual and is a large part of why the system spread.