Indexes are like card catalogs. Someone has searched the Internet, located resources, evaluated them, and classified them into catagories such as Science, Computers or Education. Yahoo is an example of an Index. Search engines are huge databases. As you enter information that you are interested in finding, the search engine finds all Web pages that are in its database that have information about your match.
Search engines use programs called spiders or bots to record content of Web pages as it goes.
Examples of search engines are Alta Vista, Excite, HotBot and Infoseek. Meta-search engines do not use their database. They use the databases and search programs of other search engines and indexes. As you enter a keyword, it sends it to multiple search engines and indexes. Each service has specific rules to help you narrow down your search.