Not quite sure how ENS works? Check out this quick video intro to ENS. Want to start on a testnet? Check out this how-to guide for testnets.
Make sure your Metamask is pointing to the mainnet. Head over to the official ENS domain name manager, and search the domain you want. If your name is unavailable you will be able to try to solicit the domain (offer the owner funds for the name). Otherwise, it should look like this.