Search engines index web pages through a process called web crawling. Automated programs, known as crawlers or spiders, visit websites to gather information about their content, structure, and links. This data is then organized in a database, where it can be easily retrieved during search queries. Search engines analyze page relevance using algorithms that consider various factors, like keywords and backlinks. Regular updates to the index ensure that search engines provide accurate and relevant results to users, reflecting the ever-changing web landscape.