A Web site is really nothing more than a set of computer files stored on a computer referred to as the server, or host. Any kind of computer can be a server, from your own PC to a large mainframe at a corporation or Internet service provider (ISP) that hosts many large and complex Web sites. Web sites are composed of Web pages; each page can contain many types of multimedia data, including text, pictures and video. The main introductory page of a Web site is called the home page.

To use the Web, you need a program called a browser. The two main browsers in use today are Microsoft's Internet Explorer and Netscape Navigator. Both are free. When you open the browser, you get a window with various command functions along the top, including a small field called "Location" (in Navigator) or "Address" (in Explorer). This field shows the URL (which is pronounced u-r-l and stands for "Uniform Resource Locator") of the Web page or other file being viewed. To get to a Web page, you enter the URL for the page you want in this field.

URLs

A URL is the way we identify a Web page, as in the following example:

Each URL has four parts:

• Every Web page begins with http://, which is how the browser knows to look for a Web page instead of some other type of file. (Browsers can open other types of files as well.) If you don't enter http://, the browser just assumes you are looking for a Web page.

• The "www.youthlearn" part of our example identifies the "domain" that houses the Web page or file. A domain is simply a set of computer resources. One computer can be a domain, or many domains can be housed on a single computer. Not all Web sites use the "www" part, and in some rare cases, the name without the w's can be a different site from one with the w's. Most of the time, however, you don't need to enter the w's, but if you have a problem finding a site, try it both ways.

The ".org" in our example is called a Top Level Domain (TDL). The domain name for our site is www.youthlearn.org. (The name "www.youthlearn.com" would refer to a different domain. TDLs are similar (but not identical) to file format extensions, and every URL has one. TDLs are determined by the Internet Corporation for Assigned Names and Numbers ICANN, the main organization that sets Internet standards. Today, six primary TDLs are in use:

• .com is mainly for commercial entities such as businesses.
• .org is mainly for nonprofit organizations.
• .net is mainly for telecommunications and Internet-type service providers who own a large network.
• .edu is mainly for schools and universities.
• .gov is for government entities.
• .mil is for military agencies.

ICANN recently created several new TDLs:
.aero is for the air-transport industry
.biz for businesses
.coop for cooperatives
.info is unrestricted in its use
.museum for museums
.name for registration by individuals and
.pro for professionals—accountants, lawyers, and physicians

These domains are not widely used yet.

In addition, dozens of TDLs are specific to countries. For example .uk refers to the United Kingdom, and .sp refers to Spain. Country TDLs are special cases, and the different national governments administer who gets to use them.

Here's the tricky part: In general, no laws control what type of TDL you can use. A nonprofit organization can use .edu or .com, and to protect their trademarks, most companies buy the .org and .net TDLs for their company names as well as the .com TDL. When you're trying to find a Web site, though, you can start by assuming that the TDL refers to the kind of organization you're looking for. If you're trying to find Howard University, for example, try "www.howard.edu"; for Disney, first try "www.disney.com".

In case you're curious, people pay a registration company for an annual license to a domain name in order to keep the system organized and manageable and so that two organizations cannot own the same domain name. Because it's a renewable license, if a company goes out of business or doesn't pay its annual fee, the domain name goes back into circulation and someone else can get it. With the explosion of new Web sites over the past few years, it's becoming harder and harder to get the exact domain name you want because someone else may already have it. That's why some organizations have to use variations of their actual names in their domain names.

Everything after the TDL (that is, what follows the ".org/" in the example above) simply identifies the specific name and location of the particular Web page or file you are viewing. The slash marks (/) separate directory names on the computer where the file is housed, and the part after the slash identifies the file name. In our example, it means you are looking at a file named "approach.html" in the subdirectory "learning" of the domain "www.youthlearn.org."

Hyperlinks

Hyperlinks, usually just called "links," are important to making the Web work for so many people. Links let you move around from page to page and site to site automatically, without entering a URL by hand. You just click on the link, which tells the computer to go to a new URL or download a file.

The links work because Web pages are written in a computer language called HTML, which stands for HyperText Markup Language (HTML). Your browser decodes the HTML in order to display the page on your screen. Other languages, such as Java and XML, make the Web work, too, but you don't need to worry about any of that at this point. The browser does all the decoding work, although you can learn about the technical mechanisms if you wish. You don't even need to understand HTML to (create a Web page)[5.4]. Simple Web publishing programs let you combine the elements you want and then automatically convert the documents to HTML for you.

Web pages do not have to be connected to the Internet. Many organizations create internal sites, usually called intranets, that are only accessible to people on their private networks. You can also have kids create Web pages that reside on your lab computers without connecting them to the Internet.

For the most part, the Web hides its underlying technology from the user so that 'the average person needs to understand little of the technology. When you access a Web site or click on a link, your browser locates and brings you the information. You do not have to worry about where the information is located, and the browser manages all storage, retrieval and navigation tasks automatically.

More About Browsers

Browsers do much more than simply display Web pages. Most have built-in functions for using email and other messaging applications, and you also can use them for downloading, opening and viewing a variety of file formats.

One way browsers do this is by associating certain file formats with other programs. For example, when you click on a link to download an ".au" file, which is a format for audio clips, the browser looks to see which application it should use to play that file when it reaches your computer. Browsers come with default settings to handle the most popular types of file formats, but you can change those settings if you prefer to use a different program.

In addition, you may encounter files that your browser doesn't know how to open, so you'll have to tell it which software to use. For example, portable document format (PDF) files are popular on the Web. The file format was created by Adobe Corporation to let people transfer heavily formatted documents (such as those that include colors, fonts and graphics) between computers that may not have the programs necessary to display them. To open a PDF file, you'll need Adobe's Acrobat Reader, which is free at Adobe's site in it's basic version. We recommend that you install Acrobat on your lab's computers because the PDF format is so popular. If you have not installed Acrobat Reader, your browser will prompt you to tell it which software to use when you try to download or view a PDF file.

You can explore all the functions of your browser on your own, but one that we want to highlight is called "bookmark" in Navigator and "favorites" in Explorer. Use bookmarks frequently to keep a record of the sites you visit often or that you want to remember for later review or research. Your browser can store an unlimited number of bookmarks.

Navigating the Web

The Web allows you to find millions of pages and reach millions of people with the click of the mouse. That makes it a phenomenal resource, but it can sometimes be difficult to find just what you want. Kids, especially, can become frustrated when they don't find what they're looking for easily and can get lost in all those links.

Luckily, many resources are available on the Web to help find you what you want; the most common tools are search engines and directories. The distinction between the two has become blurred, but in a nutshell, a search engine treats the Web like a database. You enter a word, and the engine searches the Web to find pages or files that mention or are related to that word or phrase. Different search engines use different kinds of technology to find different kinds of files and information. For example, some search engines focus on finding graphics or sounds. Directories, in contrast, may or may not be based on search engines; directories are developed by human editors, who categorize sites to make it easier to find resources on a general topic, much like the library's card catalog. Another resource is to find sites called portal sites, which bring together a wealth of information on a particular subject. Those sites almost always contain directories of links to sites about that topic and subtopics. Find out more about search engines, directories and links to learning resources.