Please forgive my ignorance beforehand. I've never before messed with network coding.

Can someone help me understand how exactly information gets from one computer to another through the internet. Here's an example of what I don't understand.

I understand how information goes between the web and Computer A, because (in a very simplified form) other computers in the web just "dial" Computer A's IP address.

The bit I don't understand is this: Computer D sends a HTTP request to some server on the web. That server sees the request as coming from (in this example) 56.78.91.23, correct? So then the server send the information to that IP. How does the router know that it is in fact the computer located at 192.168.0.4 that wants that information?