Search engines allow users to search vast databases of internet content. They work by using web crawlers to index website content and store it in a searchable database. When a user enters a search query, the search engine software returns relevant results from the database. There are three main parts of a search engine: the spider or web crawler that indexes content, the database index that stores the content, and the search software that returns results. Common types of search engines include general search engines that index all types of content, and specialized search engines that focus on specific topics, domains, or media types like images or video.