With the rapid growth of the internet and the huge amount of both IPv4 and IPv6 addresses it would be impossible to remember all IP addresses for the sites you would want to visit. This is where DNS, or Domain Name System comes into play. This can be though of as the address book to the internet.
Each device connected to the Internet has a unique IP address which other machines use to find the device.
DNS servers eliminate the need for humans to memorize IP addresses such as 192.168.1.1 (in IPv4), or more complex newer alphanumeric IP addresses such as 2400:cb00:2048:1::c629:d7a2 (in IPv6).
The domains one purchases and uses for their respective websites are mapped to an IP address. That way when a particular address is typed in ones browser, you are taken to the respective website through the resolution of that domain to an IP address.