It’s called NIP-05 verification. You can follow my guide here to set one up yourself https://orangepill.dev/nostr-guides/guide-to-verify-nostr-profile-nip05-identifier-with-your-domain/

Or you can contact NIP-05 service providers to get one. I provide one on my domain orangepill.dev if you would like me to set one up for you for a quick onboarding experience.