A web search engine is a tool that helps users find information on the internet. It works by indexing billions of web pages and using algorithms to determine the most relevant results based on a user's query. Popular search engines include Google, Bing, and Yahoo. When a user types a question or keyword into a search engine, it quickly scans its index and displays a list of links to relevant websites. This process allows people to access a vast amount of information, from articles and images to videos and maps, all within seconds.