I’m just a straight male. Are my pronouns he/him?

Probably. Straight is the wrong word here - that refers to your sexuality, not your gender identity. A straight male is into women. But a straight male could also have pronouns other than he/him. Usually, a cisgender male uses he/him pronouns, but not always. Cisgender is a word that means that your gender identity matches your assigned gender at birth - e.g. not transgender

Is that how I should tell people?

Yes, the best way to do it is part of your introductions, like, “Hi, I’m Blake, my pronouns are he him”. Usually people don’t “say” the slash, it’s just a space, but you can say it if you want.

Do you actually tell them as you meet them ?

It’s up to you. If I am meeting someone 1:1 for the first time, I probably wouldn’t unless they did first. I always do it when I’m introducing myself to a group.

Do I have to wait for a certain social cue ?

The only social cue is simply, “what are your pronouns?”. Ideally, we (cisgender folk) should be trying to make it easier for transgender/non-binary people by sharing our pronouns, even if they would be obvious to most people - I’m a hairy, 6’4” bear, most people can tell I identify as male, but if I say my pronouns are he/him or any/all pronouns (I don’t mind which pronouns people use for me) it makes it less awkward for trans people or gender non-conforming (GNC) folk to do so.

How about online. Should I tell people or have it on my personal profile somewhere?

It’s up to you, nobody will expect it from you - it’s personal information after all. If you’re comfortable sharing it, then you can put it anywhere you like, including on your profile, or you can share at the point it becomes relevant.

And about respecting other people’s pronouns. How do i figure them out?

Either they tell you, or you ask them! It’s better if you avoid trying to guess. If you need to use a pronoun and you haven’t been told them, go with they/them.

Is it a big faux pas if I don’t before I know them ?

Nope, not at all! No one is expecting you to know their pronouns before they tell you, or you ask.

Is it a faux pas if I refer to someone I just met and I assumed to be male as he/him?

Usually not - most of the time, you probably can guess from gender expression, and you wouldn’t cause any offence. If there is even 1% doubt in your mind though, you should definitely just ask. Even if you’re 99.99% or even 100% sure, it’s good to ask anyways. The more we normalise people asking and sharing pronouns, the less awkward it becomes for everyone!

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?

In my experience, it’s pretty uncommon, but it does exist. Usually they’re used by people who don’t really feel comfortable identifying as exclusively male or exclusively female, or by people who want to subvert or oppose the usual gender binary.

Hope this helps, thanks for being open with your questions and for trying to make the world a better place! If you have any other questions just ask.