A domain name system (DNS) works as the Internet's phonebook, translating human-friendly domain names (like www.example.com) into IP addresses that machines understand. When a user types a domain name into their browser, a DNS query is initiated, which travels through a series of DNS servers. These servers query each other until they find the corresponding IP address. The returned IP address allows the user's device to connect to the desired server, facilitating the access of websites and online services. DNS provides essential functionalities like caching to improve loading times and reduce traffic.