When purchasing an annual Premium Package, you receive a domain coupon to register a domain name for free.
To claim your free domain:
Go to your premium website Dashboard.
Click the GET YOUR FREE DOMAIN button.
Search for your desired domain name: type the name (without www) and select the domain TLD from the free list.
If the domain is available, you can claim it and connect it to your website.
Read about Why Do You Need a Custom Domain Name?
If you need help choosing a domain name, check out the 10 Best Tips For Choosing a Domain Name.