It all begins with HTTP
What is it?
The Hyper Text Transport Protocol (HTTP) is how the "web" works. It's how your web browser gets stuff. But if you're going to write a web application, you're going to have to understand how it works - the basics, at least.
So, you go to your browser, and type in "google.com", and up pops a page, right?
Except... it's not just "google.com" that shows up in the address bar, is it? It's got "http://google.com/". This URI tells your computer which server to connect to, and what to ask form.
URIs are used for a lot more than just HTTP, but for now, let's stick with just that. So, for the protocol, we have HTTP. The "host" is the name or IP of the computer we want to ask, and the resource path is the unique (to that host) identifier of what we're asking for.
The Request / Response cycle
So, we tell the browser we want http://google.com/ ... what does it do then?
First, it looks up the IP address for that name, then opens a connection. It then passes a request, telling the host what it wants:
GET / HTTP/1.0 Host: google.com
The host will then determine if it has a resource matching that path, and give a response accordingly:
Status: 200 OK Content-Type: text/html ...
And that's it. One request - one resource.
But wait, you say... what about the images and other things? Well, when your browser reads through the HTML, it finds tags that tell it to go fetch other resources. So it will do so with separate requests. Again: One request - one resource.