How Do Search Engines Like Google Work?
How Google works:
Google works by scanning or ‘crawling’ the millions of websites on the internet and gathering important information from these sites about their content and how helpful they will likely be for users interested in this topic.
Google has a software crawler, referred to as a spider or bot. This spider regularly goes out and crawls websites available online. When it lands on a website, it picks up important data markers, including important key terms that indicate the topics covered, traffic to the site, how the site is constructed, and how relates to other sites on the topic. It then uses the information to process its algorithm.
Websites get crawled regularly, without any input from website owners. Sites that receive high amounts of traffic and regular updates will naturally receive more frequent crawls than those who do not have either of these traits.
Website owners do have the ability, however, to request that Google crawls their page if they post an important update or piece of content and they do not want 
to wait for the search engine spiders to notice it naturally. Websites and individual web pages will only be added to the index once they have been crawled, so requesting a crawl on websites can be valuable for those who want to get their material noticed and in front of potential users on the search engine.
The Google algorithm is a sophisticated calculation that takes in countless data points from millions of websites online and computes their relevance to the queries that users type in. When someone asks Google a question, the algorithm computes the relevance of the different sites using the data points the spider collected. The result it returns to the user is known as the search engine results page, or SERP.
The algorithm remains highly confidential, unknown to people outside of the company. Marketers, however, have used a variety of tests and experiments along with conversations with Google representatives to better understand the types of factors Google takes into account.
Through these conversations and tests, we know that the algorithm cares about factors such as page speed, mobile friendliness, keyword and content relevance, and domain authority.
The Google algorithm does not remain static. The search engine regularly looks for ways to update the algorithm to better reflect the needs of users. Its goal remains to provide users with an optimal experience so they will continue to use the search engine. For this reason, the search engine wants to refine their ability to understand user intent and website content. When they make these changes, you will hear marketers refer to algorithm updates. Often, these updates result in shakeups regarding how highly pages rank for different types of queries.
