ENS works with two kinds of names: .eth names, registered in the ENS App, and DNS domains such as .com, .org or .xyz, imported from where you already own them.
A DNS domain's ending (TLD) must come from the ICANN root, such as .com, .xyz or a country code like .uk. Some endings, such as .box, run their own ENS setup outside the usual import; the ENS docs list them in Supported TLD List.
What's the difference between .eth and DNS names?
A .eth name is native to ENS: you register it in the ENS App and pay an annual ENS fee. A DNS name is a regular internet domain that you own already and import. Once imported onchain, it works like a .eth name inside ENS: it points at a wallet and holds records like avatar and social handles.
To import a DNS domain, use ENS Explorer: see Import a DNS name. The ENS App doesn't do this. Onchain imports run on ENS v1 for now.
Do imported DNS names need ENS renewal?
No. There's no ENS fee and no ENS renewal; you pay only your DNS registrar, plus gas for an onchain import. A .eth name is the opposite: you pay ENS each year. See Pricing, fees and multi-year discounts.
What happens if my imported DNS domain expires?
The ENS side never expires, but the DNS domain at your registrar does. Whoever holds the domain next can change its ENS TXT record (a text entry in the domain's DNS settings) to point at their own wallet, and that hands them the ENS name. Keep your DNS domain active to keep control; Can I use my DNS domain as an ENS name? explains how DNS control works.
Does ENS sell DNS domains?
No. Buy a DNS domain from a DNS registrar, then import it. To register a name through ENS itself, see Register a .eth name.