All search engines use their own web crawlers to examine hundreds of billions of pages. A search engine navigates the Internet by downloading web pages and following the connections on these pages to discover newly accessible pages.
Web content databases that can be queried are known as search engines. They consist of two major components:
Search the index. A database containing information about websites.
The search algorithm (or algorithms). Computer program(s) charged with matching search index results.
There are three principal functions of search engines:
Crawl: Search the Internet for content, examining the code and content of each URL discovered. Crawling is the procedure that search engines use to uncover new and updated content. This content may be a web page, an image, a video, a PDF, and so on. Only if it is linked to another item of content can it be located.
Index: Store and organize the content discovered during crawling. Once a page has been indexed, it will be displayed in response to pertinent queries.
Rank: Provide the content that best answers a user's search query in an ordered list. The order of the results is from most relevant to least relevant.
How Search Engines Work
Google's two categories of web crawlers are known collectively as Googlebot.
Googlebot Desktop is a desktop crawler that mimics a desktop user.
Googlebot Smartphone: a mobile crawler that mimics a mobile device user.
Googlebot begins by retrieving a few web pages, which are typically pages from a sitemap so that Google knows they exist, and then it follows the connections on those pages to discover new URLs. Using this path of links, the crawler is able to discover new content and add it to their index, a vast database of discovered URLs, so that it can be retrieved when a user searches for information that is a good match for the content on that URL.
Search engines process and store information they discover in this index, a massive database of all the content they've discovered and the content they deem to be the best for displaying on their SERP.
When a user conducts a search, search engines comb their index for highly pertinent content and then arrange it, in an attempt to answer the user's query. Ranking refers to the ordering of search results by relevance. In general, the higher a website is ranked, the more pertinent the search engine considers it to be to the query.
The SEO community only pays attention to Google, despite the existence of more than 30 main web search engines. This is because Google is the most popular search engine on the web. Google has always been approximately 20 times more popular than Bing and Yahoo combined.
Consequently, ensuring that your website is crawled and indexed is required for it to appear in the SERPs. If you already have a website, you may want to begin by determining how many of your pages are indexed. This will provide valuable insight into whether Google is crawling and discovering all of the pages you want it to and none of the pages you don't.
One method for examining your indexed documents. Enter "site:yourdomain.com" into the search bar on Google. This will only yield results from your site that have been indexed by Google.
How Search Engines Work
Complex mathematical algorithms are used by search engines to interpret which websites a user pursues. Websites with more incoming links, or stronger links, are assumed to be more significant and relevant to the user's search.
In addition to their URL submission console, Google provides Google Search Console, for which an XML Sitemap feed can be created and submitted for free to ensure that all pages are found, particularly pages that are not discoverable by automatically following links.
When crawling a website, search engine crawlers will consider a number of distinct factors. Not all web pages are indexed by search engines. The distance of pages from a site's root directory is a significant factor in whether or not they are crawled.
Webmasters can instruct spiders not to crawl specific files or directories using the robots.txt file located in the domain's root directory to prevent objectionable content from being indexed by search engines, typically pages for members.
A page can also be explicitly excluded from a search engine's database by using a meta element specific to robots (typically meta name="robots" content="noindex">).
The robots.txt file in the root directory is the first file examined when a search engine visits your website. The robot is then instructed by the robots.txt file as to which pages should not be crawled.
Login-specific pages, such as purchasing carts and user-specific content, are typically examples of pages that should not be crawled.
If you have created your own search facility for your website, not the one supplied by Google, then this should not be indexed because those pages are considered search spam – the pages of your search are already being indexed, so your search box generates content that Google already has.