In its simplest form, the internet is a telecommunications system that allows computers and assorted other devices to communicate with each other using the same communications language, a protocol called TCP/IP, transmission control protocol / internet protocol.
It doesn't matter if the humans using the computers are communicating in English, French, German, or Chinese, the computers are communicating using TCP/IP. That's pretty amazing if you think about it. How many other things are done exactly the same way, everywhere in the world?
I could give a long lecture on all the nuts and bolts, and technical details, but what makes the internet possible is the common language, the protocols, that the computers speak. TCP/IP has spanned across generations of computers, using different operating systems.