Think of Nip-05 as a human readable nostr address instead of giving somebody a long string of letters and characters you give them an email like address.
on the technical side its just a json file on your web server with your username and pubkey.
Discussion
Ah cool. Where do I find NIP-05 though?
Host it yourself if you own a domain (add a file called nostr. json in your .well-known folder)
or there are a few places that can get you one for free/ cheap.
Check out https://nostr.how/en/guides/get-verified to find some providers.