All computers on the Internet are uniquely identified by an IP address. Just like a phone number uniquely identifies a particular phone, an IP address uniquely identifies a specific server. URLs are resolved to a specific server via domain naming services (DNS). A domain name service translates a URL such as www.microsoft.com into a specific IP address such as 126.96.36.199.
The simplistic discussion here about IP addresses and computer names assumes that the computers all have static IP addresses. Most home (and many business) users are assigned dynamic IP addresses by their Internet Service Provider (ISP), and DNS doesn't provide any mapping service for these dynamic addresses.
In order to connect to the Internet (unless your company is a lot larger than most), you'll need an Internet Service Provider (ISP). An ISP supplies basic services and access to the Internet for most users. Many people believe their ISP (AOL, for instance) is the Internet. That's not true, of course. Instead, ISPs are simply service providers. AOL and MSN simply dress up their services with pretty front ends and lots of hand-holding for novice users. Services from an ISP typically include e-mail, URL resolution, and content management.
You might think of an ISP as being similar to a phone company. The ISP manages a large network of computers that provide services, just like the phone service company provides basic services and a dial tone. There are many different ISPs, just as there are many different phone companies. What's more, phone companies are often ISPs, which makes a lot of sense.
Once you're connected to the Internet, you normally enter a Uniform Resource Locator (URL) into a browser to browse the Web. When you type a URL into the address box in a browser and then press the Enter key, your browser uses a TCP/IP connection to send the address to the ISP. Windows also sends the client computer's IP address. An ISP's server resolves the URL as an IP address and sends the request to the IP address (that is, a Web server computer).
The server processes the request and returns whatever information has been requested. The server uses the client computer's IP address to know where to return the information. Windows intercepts the information and provides it to the application (the Web browser).
Increasingly, applications that aren't specifically Web browsers are using Internet communications to do their jobs. For instance, you might build a complete database application that uses data stored remotely on a server computer, taking advantage of XML Web Services to retrieve the data as necessary. You will see examples of this as you work through this book.