A search engine is a website that allows users to look up information on the World Wide Web (WWW), part of the Internet. The search engine will achieve this by looking at many web pages to find matches to the user's search inputs. It will return results ranked by relevancy and popularity by the search engine. Some popular search-engines are Google Search, Yahoo! Search, Ask.com, Forestle and Bing. Older services include Webcrawler, Lycos, and Alta Vista.

To use a search engine you must enter at least one keyword in to the search box. Usually an on-screen button must be clicked on to submit the search. The search engine looks for matches between the keyword(s) entered and its database of websites and words.

After the user inputs their search or query into the search bar, a list of results will appear on the screen known as search engine results page (SERP). This list of webpages contains matches related to the user's query in a particular order determined by a ranking system. Most search engine will remove "spam" pages from the list of results to provide a better list of results. The user can then click on any of the links to go to that webpage.

Search engines are some of the most advanced websites on the web. They use special computer code to sort the web pages on SERPs. The most popular or highest quality web pages will be near the top of the list. 

When a user types words into the search engine, it looks for web pages with those words. There could be thousands, or even millions, of web pages with those words. So, the search engine helps users by putting the web pages it thinks the user wants first.

Search engines are very useful to find information about anything quickly and easily. Using more keywords or different keywords improves the results of searches.

A search service may also include a portal with news, games, and more information besides a search engine. Yahoo! has a popular portal, and MSN Search is part of the MSN portal, while Google has a simple design on its front page. Search services usually work without charging money for finding sites, and are often supported with text or banner advertisements.

Crawling 
Search engines use robots to ‘crawl’ online content. The process of crawling is the first measure that search engines take before indexing content in virtually any form–videos, text, images, webpages, etc..The content may constitute newly uploaded content to the internet or content that features updates or changes to its material. These robots, also known as crawlers or bots, record the information along with its links. Once the material has been crawled, it can be stored in a massive URL database. It’s this database that generates internet search results.

Indexing 
After the bots crawl content, it can be indexed in the database and arranged in terms of its relevance. If internet content has not been crawled or indexed, it is unlikely to appear in the search results when someone makes a query no matter how relevant that content may be. After the content has been crawled, each of its words is indexed. The search engines also pinpoint where words are located on the crawled pages. During the indexing process, the search engine compares the content to other content with similar ‘words’ and decides how to organize it within its index.

Ranking 
Ranking is a complex process that is dependent on search engine algorithms. When a searcher makes a query on Google looking for anything from 19th century British landscape painters to New York City plumbers, the search engine will generate a list of good matches to that query. How these matches appear in the list relates to its rank. The search engine lists what it ‘thinks’ are the best answers to the query early in its search results.

Google and other search engines rely on algorithms to interpret the searcher’s query, identify the websites and pages in its index that are related to the request, and it then ranks them in terms of relevance in its presented search results list. What’s important to search engines is to provide searchers with the most relevant matches to their queries as possible. Website operators, in turn, use search engine optimization to give their pages a higher rank.

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