Where can I Educate myself on PGP?

I've seen a few things about pgp and I want to try it out but I'm confused and have a few questions.

Firstly, can it be used for calls? I see sim cards for sale which advertise pgp calls but does anyone know if they're even legit? They look really shady.

Are they the same as "Russian sims" and "white sims", or is that something completely seperate?

Another thing is how secure is it? Some places say its unbreakable even …

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