A search engine is a software system designed to help users find information on the internet. It works by indexing web pages and using algorithms to rank them based on relevance to a user's query. Popular search engines include Google, Bing, and Yahoo. When a user types a query into a search engine, it quickly scans its index and returns a list of results that match the search terms. These results often include links to websites, images, and videos, making it easier for users to access the information they need.