The importance of robots.txt

When a search engine crawler comes to your site, it will look for a special file on your site. That file is called robots.txt and it tells the search engine spider, which Web pages of your site should be indexed and which Web pages should be ignored.

The robots.txt file is a simple text file (no HTML), that must be placed in your root directory, for example:

http://www.yourwebsite.com/robots.txt

As mentioned above, the robots.txt file is a simple text file. Open a simple text editor to create it. The content of a robots.txt file consists of so-called "records".

A record contains the information for a special search engine. Each record consists of two fields: the user agent line and one or more Disallow lines. Here's an example:

User-agent: googlebot
Disallow: /cgi-bin

This robots.txt file would allow the "googlebot", which is the search engine spider of Google, to retrieve every page from your site except for files from the "cgi-bin" directory. All files in the "cgi-bin" directory will beignored by googlebot.

The Disallow command works like a wildcard. If you enter

User-agent: googlebot
Disallow: /support

both "/support.html" and "/support/index.html" as well as all other files in the "support" directory would not be indexed by search engines.

If you leave the Disallow line blank, you're telling the search engine that all files may be indexed. In any case, you must enter a Disallow line for every User-agent record.

If you want to give all search engine spiders the same rights, use the following robots.txt content:

User-agent: *
Disallow: /cgi-bin

Source: http://www.businessseek.biz/article-directory/article-59.html