This video step by step shows how to buy and add a domain name using Godaddy service. In the following video tutorial user interface is outdated but the process of adding the your own domain name stays the same.

There are many other services who offer domain names.
The most important thing is to find the place where you can change nameservers.
Make sure the nameservers of the domain name are these ones:

• a.ns.berta.me
• b.ns.berta.me

You can enter them when you buy the domain or if it is already bought by logging in to the admin panel of the domain seller or sending an email to the seller with the request to change nameservers.

Enter your domain name in Berta.me hosting panel by clicking Add (next to your domain name). Voila! If the nameservers are correct, your domain name is connected to your Berta.me website!

In some cases it can take up to 48h for global DNS servers to update information.