Mostly it's chill - don't worry about it. If you make an honest mistake, no sane person will think less of you for it. The real faux pas people keep running into is usually just being a cock about this. It's reasonably easy to avoid.

You likely don't need to tell anyone IRL. You're a guy, so he/him is natural. Nobody's likely to even ask. Same applies if it's obvious online, otherwise feel free to add it in your profile or something.

And about respecting other people’s pronouns. How do i figure them out ? Is it a big faux pas if I don’t before I know them ? Is it a faux pas if I refer to someone I just met and I assumed to be male as he/him?

Most people are cis (etc) anyway, so the obvious guess is mostly safe. You rarely need to refer to anyone by a pronoun before they're introduced to you. In that case it's "they" - perfectly normal, native English for centuries, which people sometimes forget. Then, if someone's introduced as "Bob" he's probably fine with "he" etc.

If you're worried about getting it wrong, I'd just wait for a name or refer to them some other way.

I’ve never seen anyone referring to anyone irl by non conventional pronouns. Is it an actual thing or is it currently being pushed to make the world a more inclusive place?

IRL that's unlikely, neopronouns are pretty niche even on the internet. He/she/they will do in the vast majority of cases. People who insist on one of the other ones are fairly rare.