Search engines have crawlers (bots / spiders) that “crawl” the World Wide Web to discover pages that exist in order to help identify the best web pages to be evaluated for a query. The method of travel by which the crawlers travel are website links.

Content can vary — it could be a webpage, an image, a video, a PDF, etc. — but regardless of the format, content is discovered by links.

Crawlers start with a trusted set of websites that serve as the basis for determining how other websites measure up, and by following the links they see on the pages they visit, they expand their crawl across the web.

Indexing is the act of adding information about a web page to a search engine’s index. The index is a collection of web pages—a database—that includes information on the pages crawled by search engine spiders.

• Detailed data on the nature of the content and topical relevance of each web page
• A map of all the pages that each page links to
• The clickable (anchor) text of any links
• Other information about links, such as if they are ads or not, where they are located on the page, and other aspects of the context of the link and what that implies about the page receiving the link

When a user types into the search box, search engines seek their index for highly relevant content and then orders that content in the hopes of solving the searcher’s query. This ordering of search results by relevance is known as ranking. In general, you can assume that the higher a website is ranked, the more relevant the search engine believes that the site is to the query.

The effective SEO helps influence the relevance and importance of those web pages for related queries.

• Relevance: The degree to which the content on a web page matches the intent of the searcher (intent is what searchers are trying to accomplish with that search, which is no small undertaking for search engines—or SEOs—to figure out).

Importance: Web pages are considered more important the more they are cited elsewhere (think of these citations as a vote of confidence for that web page). Traditionally, this comes in the form of links from other websites to that web page, but there could be other factors that come into play as well.