A domain name is a familiar name that facilitates access to a website and replaces an IP address. In other words, a domain name is a familiar, easy-to-remember name used to identify a computer on the Internet. It looks like fun.io, iweb.com, google.ca, which is clearly easier to remember than 188.8.131.52, 184.108.40.206 or 220.127.116.11. Also, it allows the underlying IP to be changed, so the domain name can point to a different IP/server.
Generally speaking, the use of a domain name allows an easier access for your customers and users to your website.