How do you have one IP address and many websites?

How can I have it where I have one IP address that sits on the Internet but many web names? For example, when a hosting company has a shared IP but I get unlimited domain names (along with everyone else on that box).

I have a box on the Internet but I want to point to another machine that holds a different website when someone types in the different www...(it's sitting right next to it in just a different box). Is that all subdomaining? Thank you.

I am the hosting company

It's part of the HTTP 1.1 protocol.

Specifically, the HTTP 1.1 protocol includes a header called "host:" which specifies which web site on a particular server the client is attempting to access.

So, if snoopy.net and woodstock.org both share 192.0.32.10 and your browser is trying to get content from http://snoopy.net/doghouse the specific http request would look like:

GET /doghouse HTTP/1.1
Host: snoopy.net

If the desired url is http://woodstock.org/seeds the request would look like

GET /seeds HTTP/1.1
Host: woodstock.org

In both cases, there would be a tcp socket between your computer and port 80 of the server. The server would know to get content from /var/www/snoopy.net or /var/www/woodstock.org/ based on the Host header.

There would be other headers for cookies and other stuff like browser type and allowed content, but the "Host" header specifically is what allows the web server to know which virtual web site is desired.

There's more in the RFC2616.

This is also why https sites must** have their own IP address -- the ssl key exchange and certificate verification take place prior to the http transaction, so the http server won't know to give out the certificate for "woodstock.org" or "snoopy.net" when it receives an https connection on port 443 of 192.0.32.10.

edit

** in the comments Grawity points out that there are extensions to SSL in the TLS spec that allow the server to know which web site the user is attempting to access, and that most modern web browsers have these extensions, so must is a bit too strong.

There is something that all modern browser send along with the request, called the "Host:" Header.

The actual request firefox sends for this page is:

Host: superuser.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 (.NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive

As you can see, the

Host: superuser.com

As for your particular issue, you will have to read up on how your particular hosting company wants you to request the configuration.