Premium domain names are considered especially valuable because they're short, memorable, and often have popular keywords or phrases.
For example, imagine you want to start website about cute cats. Instead of having domain like "catloverblog123.com", you might go for something like "CuteCats.com". "CuteCats.com" is premium domain because it's short, easy to remember, and has exact keywords people might search for when looking for cute cat content.
You can buy premium domains on Site.pro:
Go to My Websites;
Select "+ Add domain", choose "Buy new domain";
Write your domain name;
Select domain name with blue label next to it that says ‘Premium’ and click ‘Buy’.