If you already bought a domain, maybe years ago, maybe last week, before you'd settled on a website builder, it's a fair question whether that purchase was wasted or whether you can still use it. Across most website builders, the short answer is generally yes, though how well it works and what it takes depends on the specific platform.
Connecting an existing domain to a website builder usually means one of two things technically. Some platforms want you to update your domain's nameservers, pointing your domain's management entirely at the new host. Others ask you to add specific DNS records, often a CNAME or A record, at your current registrar, which lets you keep managing the domain where you bought it while pointing just the website traffic at the new platform. Neither approach is complicated once you know which one a given builder expects, but it does usually mean logging into wherever you originally bought the domain, GoDaddy, Namecheap, or elsewhere, and making a small change there.
Where this gets specific to Nova: the paid plan supports a custom domain and can handle buying and setting one up for you if you don't already have one. If you already own a domain from another registrar and want to connect that existing one instead of buying new, check Nova's current domain settings directly to confirm the process, since the exact steps for connecting a domain you already own are worth verifying at the time you're ready to do it rather than assuming based on how any other builder handles it. In the meantime, you can build and preview your site on a free getnova.pro subdomain without needing to resolve the domain question at all, which means an already-owned domain doesn't have to be sorted out before you start.
Not necessarily, most website builders support connecting a domain you already own, though the exact steps vary by platform. It's still worth confirming directly with whichever builder you're using before assuming it works a specific way.
Changing nameservers moves all of your domain's management to the new host. Adding a DNS record, often a CNAME or A record, lets you keep managing the domain at your original registrar while pointing website traffic elsewhere. Which one you need depends on the specific platform's instructions.
Yes, you can describe your site to Nova and preview it on a free getnova.pro subdomain without connecting any domain at all, and sort out the domain question once you're ready to publish for good.
Describe your site to Nova and worry about the domain question once you've seen what you're actually building.