Hello, I want to use a PGP key with my Proton mail account.
I was wondering how using PGP works exactly. Does it encrypt the whole email message? Or is it only a signature to prove it’s origin?
How does it affect recipients if they don’t have my public key? Or how do I share that key securely?
Signing an email generates a string that can be used with your public key to verify the contents haven’t been tampered with and that it came from you (assuming that you haven’t leaked the private key).  Encrypting an email is a different process; you’ll need the recipients public key, and they will decrypt with their private key.
The intent of the design of public key cryptography is that the public key can be shared freely without risk.
Ah ok, so it’s like a MD5 sum of the email with a signature key then.
Are you trying to use an email client for proton mail without paying for plus?
No I have a paid subscription. But I’m using their Android app, as well as Thunderbird in Linux.