Search engines:

Search engines allow users to search the internet for content using keywords.
User can search for any information by passing query in form of keywords or phrase. It then searches for relevant information in its database and return to the user.
Although the market is dominated by a few, there are many search engines that people can use.
Searching content on the Internet becomes one of the most popular activities all over the world. In the current era, the search engine is an essential part of everyone's life.
To display search results, all search engines first find the valuable result from their database, sort them to make an ordered list based on the search algorithm, and display in front of end-users. The process of organizing content in the form of a list is commonly known as a Search Engine Results Page (SERP).
Search engines often change their algorithms (the programs that rank the results) to improve user experience. They aim to understand how users search and give them the best answer to their query.

=>some popular examples of search engines are following :

Components of search engine:

User interface: it is form with control so that user can enter the text related to the information.
Parser: is a query and divide it into words to create some meaningful combinations about your searching word.
Searcher : Searcher will search all the document.
Evaluator: it will evaluate the result of your searching word.
Gatherer: will collect the result set submitted by searcher and returns result set with document indexer.
Indexer: will arrange the clickable URLs returns with documents in descending order and generates index of user.

As we all know it is widely used over internet.
In a search engine user can put his text it is called query, into form called user interface.
After typing query when user click on search button then query will pass to parser.
Parser will divide the query into different words. It generate their combinations and submitted result to searcher.
Then searcher will search all the document matching with combination and returns the result set to èvaluator.
Now evaluator will evaluate the matching of records within returned result set and assign score from1 to 100 and submits the result to Gatherer.
Gatherer is responsible to collect all the documents based on the evaluation done by evaluator and it pass to indexer.
Indexer will now create index of all the documents in descending order of relevancy score and display score to user, then after user can select any number of hyperlink to search information.
In this way searching is done by search engine.