The first step to finding useful information is expecting that information exists. Next, learn to use search engines. An index is just that, sites are submitted and essentially approved for listing. The differences between indexes and crawlers become more apparent when using them. Indexes allow you to search catagories, as pages are organized when they are listed.
Crawlers only offer free text searches, which scan for chunks of text and keywords.
Crawler keywords are defined by the HTML authors on the page, index Keywords are defined when the site is submitted. Details about embedding keywords are available on Alta Vista's help page, and I'm sure the other crawlers explain how they record pages as well. Alta Vista offers much more freedom in searching, I often wish I had an Alta Vista search for everything I read. After a little practice, you learn how to search for any string of text, even if it's as obscure as the middle word of a sentence and one word of the title. There are dozens of search engines now, and at this point, it's mostly preference as to which one will work best for you.