At its most basic, technical form the Internet is a vast series of interconnected computers, each with a different function or service to provide. One computer might be dedicated to sending or receiving e-mail while another might be dedicated to serving a particular website.
Nobody really knows, but it is certainly well into the hundreds of millions.
Now, you may well be wondering how all this information travels from point to point along the Internet. The best way to answer this question is to have you think about a tree. Yes, a tree. Think of yourself as a small branch. The trunk is connected to literally hundreds of other branches.