Please note, that you need a Pro account to be able to connect a custom domain to your website.
First, you need to purchase a domain name from your favorite domain provider. Some of the best ones are domain.com, godaddy.com, or namecheap.com. After you have successfully purchased your domain you need to set the following A record on your DNS provider to contain these values:
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Godaddy.com - https://ie.godaddy.com/help/add-a-cname-record-19236