Also look at some people you know and who they follow. 

Yeah anyone can get a NIP05. Some people you know own a certain domain would be the only ones who can id themselves with that domain. 

Other people you might just have to do a little bit of work. 

 agree. getting your own domain makes most sense. is there a good tutorial somewhere? would love to auth with cal.com 

 It seems like cal.com is not fully translated to Portuguese.
I am available to help you with that work.
Let me know. 

 here we use nip 05 to connect domains to our profiles as a unique identifier… which will earn you a check. The more notable your url the more verification it provides. 

Here is the official nip (nostr implementation possibility)
https://github.com/nostr-protocol/nips/blob/master/05.md

and a guide on how to set it up yourself
https://orangepill.dev/nostr-guides/guide-to-verify-nostr-profile-nip05-identifier-with-your-domain/

There are also services like https://nostr.directory and https://nostrplebs.com that offer simpler methods of obtaining an identifier. nostrdirectory Derek Ross 

 agree. getting your own domain makes most sense. is there a good tutorial somewhere? would love to auth with cal.com 

 It seems like cal.com is not fully translated to Portuguese.
I am available to help you with that work.
Let me know.