A domain name is a human-friendly address, sometimes called a URL. The internet uses IP addresses, which are numbers, much like a telephone number. Most people find it much easier to remember names rather than strings of numbers. Companies, like Web Africa choose to publicise their domain name (https://www.garanntor.com) rather than their IP address (188.8.131.52).
Your domain name is unique to you and when someone types it into an Internet browser they will be taken directly to your space on the Internet where they can view your site.
Having your own domain name is also quite useful would be when creating an email address, you could have choose a fun and innovative email address such as firstname.lastname@example.org or a business appropriate email address.