What is a search engine?Search engine is a web application tools sometimes integrated with browser e.g., Google Chrome.The major objective of search engines is to match user queries with search results for example Google’s motto is to provide best possible results to users online. Every search engine aims to provide the best, most relevant results for users.Any search engine has three components:Search crawler otherwise known as botSearch index a database of webpagesSearch Algorithm to rank websitesThe key functions of search engine are to crawl, index and rank search results using rank algorithm.How do search engines make money?Before we understand how search engines make money, we need to understand the structure of search engine result page. The Search engine result page or SERP’s consist of various types of results.Google search results that appear on Google’s result page into 6 types, each having their own subtypes.Knowledge Graph Panel and Knowledge Card.Local search results.Rich results and featured snippets.Related searches.Regular organic results.Non-organic results (paid results, shopping ads)These results can be classified into two broad typesPaid results – This is the space where Advertisers pay per user click to have their products and services Ads to Ad Networks like AdWords. This is also the section on SERP where search engines make money from. Google Ads running on basing on campaign types can be classified into five different types of ad campaigns with Google Ads: Search (text ads on Google search results)Display (image ads on websites)Video (video ads on YouTube)Shopping (product listings on Google for Product searches)App (your app promotion on many channels)Search Ads as the name suggests are triggered by user queries when people search on Google, text ads can appear above or below the search results. Only up to four ads are eligible to show above the search results. Ads typically appear along the edge of the page (like the top, side, or bottom). How they’re matched: Google matches ads to a person’s search based on how closely the search matches your keywords and campaign settings Organic results – These are results you can’t pay for to be there. Organic results are listings that have been indexed by the search engine based on several factors, also known as “ranking signals.” This is where search engine optimization comes into action. While paid search focuses on optimizing ads to be shown in as prominent a position on the SERP, SEO’s work on content, on Page, off page and other factors like social signals to rank results possible.Why should you care how search engines work?Understanding how search engines find, index and rank content will help you to rank your website in organic search results for relevant and popular keywords. If you can rank high for these queries, you’ll get more clicks and organic traffic to your content.How search engines build their indexMost well-known search engines like Google and Bing have trillions of pages in their search indexes. So, before we talk about ranking algorithms, let’s drill deeper into themechanisms used to build and maintain a web index.Here’s the basic process, courtesy of Google:Let’s break this down, step by step:1. URLs2. Crawling3. Processing & rendering4. IndexingSidenote.The process below applies specifically to Google, but it’s likely very similar for another websearch engines like Bing. There are other types of search engines like Amazon, YouTube,and Wikipedia that only show results from their website.Step 1. URLs:Everything begins with a known list of URLs. Google discovers these through variousprocesses, but the three most common ones are:From backlinksGoogle already has an index containing trillions of web pages. If someone adds a link toone of your pages from one of those web pages, they can find it from there. From sitemapsSitemaps list all the important pages on your website. If you submit your sitemap toGoogle, it may help them discover your website faster.From URL submissionsGoogle also allows submissions of individual URLs via Google Search Console.Step 2. Crawling:Crawling is where a computer bot called a spider (e.g., Googlebot) visits and downloadsthe discovered pages.It’s important to note that Google doesn’t always crawl pages in the order they discoverthem.Google queues URLs for crawling based on a few factors, including:the PageRank of the URLhow often the URL changeswhether or not it’s newThis is important because it means that search engines might crawl and index some ofyour pages before others. If you have a large website, it could take a while for searchengines to fully crawl it.Step 3. Processing:Processing is where Google works to understand and extract key information fromcrawled pages. Nobody outside of Google knows every detail about this process, but theimportant parts for our understanding are extracting links and storing content forindexing.Google has to render pages to fully process them, which is where Google runs the page’scode to understand how it looks for users.That said, some processing occurs before and after rendering—as you can see in thediagram.Step 4. Indexing:Indexing is where processed information from crawled pages is added to a big databasecalled the search index. This is essentially a digital library of trillions of webpages where Google’s search results come from.That’s an important point. When you type a query into a search engine, you’re not directlysearching the internet for matching results. You’re searching a search engine’s index ofweb pages. If a web page isn’t in the search index, search engine users won’t find it. That’s why getting your website indexed in major search engines like Google and Bing is so important.BacklinksBacklinks are one of Google’s most important ranking factors.Andrey Lipattsev, Search Quality Senior Strategist at Google, confirmed this during a livewebinar in 2016. When asked about the two most important ranking factors, hisresponse was simple: content and links.Absolutely. I can tell you what they [the top two ranking factors] are. It is content. And it’slinks pointing to your site.Links have been an important ranking factor in Google since 1997 when they introducedPageRank, a formula for judging the value of a web page based on the quantity andquality of backlinks pointing to it.When we analysed over one billion pages, we found a clear correlation between thenumber of websites linking to a page and the amount of organic traffic it gets fromGoogle.However, it’s not all about quantity because not all backlinks are created equal. It’sperfectly possible for a page with a few high-quality backlinks to outrank a page with lotsof lower-quality backlinks.What makes a good backlink? There are six key attributes of a good backlink.Link authorityBacklinks from authoritative pages and websites usually have the most impact onrankings.How do you define authority? In the context of SEO, authoritative pages and websites arethose that have many backlinks or “votes.”In Ahrefs, we have two metrics for estimating the relative authority of websites and pages:Domain Rating (DR): The relative authority of a website on a scale from 0-100.URL Rating (UR): The relative authority of a page on a scale from 0-100.