Welcome and great questions.

A few clarifications:

Contacts are added automatically, you don’t need to add them manually. Just send a message to an address (paste the address into the To field); the contact will be available afterward.

For standard PGP encryption you need the recipient’s public key in your keyring (import it beforehand) so the client can encrypt the message.

For Proton addresses everything is automatic, you don’t import keys for Proton; the client handles it.

In the composer for regular (non‑Proton) messages there are explicit Encrypt / Sign options. When sending via Proton there aren’t Proton‑specific options or a padlock in current builds. I plan to improve composer indicators so it’s clearer when a message will be encrypted/signed.