If you don't have a domain name, then buy one - go to www.namecheap.com or any similar service of your preference and follow their instructions.
Make sure the NAMESERVERS of the domain name are these ones:
You can enter them when you buy the domain or if it is already bought by logging in to the admin panel of the seller or sending an email to the seller with the request to change nameservers.
Enter your domain name in berta's website manager by clicking "add" (next to your domain name). Voila! If the nameservers are correct, your domain name is connected* to your berta website!
- in some cases it can take up to 48h for global DNS servers to update information.