A few years back, Google had a great microsite entitled “How Google Works.” It was so well presented that I took screen shots of the site to share with others in workshops. The latest version is called How Search Works, and I’ll include screen shots from that here. There are two main tasks that search engines perform: indexing and ranking.
Indexing is the reading and storing of a web page’s information by the search engine indexing robot (in this case, GoogleBot). Once Google visits and reads a page, it stores that information in its index. I like to imagine the index as a huge library, like the Jedi Library from “Star Wars.”
Ranking is the process where the search engine evaluates the information in its index and determines which web pages match its criteria according to the search query and other factors (such as device). A site cannot be ranked, however, if it is not already indexed. Ranking is like the librarian, providing recommendations based on your criteria.
I find it common that articles will conflate indexing vs. ranking factors, and it’s important to remember that these are two different things entirely. Ultimately, indexing is the foundation. If you do not have a page indexed, then it cannot be ranked.