More advanced servers add security to allow an encrypted connection between server and browser so that sensitive information like credit card numbers can be sent on the Internet. The whois form at Network Solutions allows you to enter a domain name on a form, and the page returned is different depending on the domain name entered. Any search engine lets you enter keywords on an HTML form, and then it dynamically creates a page based on the keywords you enter. It is actually processing information and generating a page based on the query. In almost all cases, the web server is using something called CGI scripts to accomplish this magic.
Search engines have three major elements.
First is the spider, also called the crawler. The spider is essentially a program that visits a web page, reads it, and then follows links to other pages within the site. The spider returns to the site on a regular basis, such as every month or two, to look for changes. Everything the spider finds goes into the second part of a search engine, the index. The index, sometimes called the catalog, is like a giant book containing a copy of every web page that the spider finds.