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

There’s lots to sort through, humans are complex beings. But you can break it down into simple chunks. You’re straight - but this actually has no direct effect on your pronouns. You identify as ‘he,’ so your pronouns are he/him.

Is that how I should tell people?

If you want people to refer to you as a ‘he,’ then yes. He/him is correct.

Do you actually tell them as you meet them ? Do you actually tell them as you meet them ? Do I have to wait for a certain social cue ?

It depends on the individual’s social expectations, like other conversation matter. Generally you will be fine not immediately offering your pronouns if you identify as a ‘he,’ you present as a ‘he,’ and others recognize you as a ‘he.’ However it is polite to offer your pronouns when others have offered theirs or asked someone else’s. Some situations may formally ask for pronouns and some circles may standardize it as a part of their conversations, and other times it comes up impromptu.

Being cool with and accepting of using pronouns simply prevents awkwardness/imbalances/double standards/a spotlight on anyone who ‘sticks out.’ This isn’t likely something you have to deal with, but that’s why it’s all the more meaningful when you can comfortably navigate these discussions for the sake of those have more complex identities - it helps them to feel their belonging. At the same time I’m not aware of any common expectation that you would initiate pronoun sharing unless your were an organizer of some sort. Of course it would be kind of you to initiate it if you’re in a situation where you think it might spare someone discomfort (e.g., to pre-empt ptoential misgendering of someone with pronoun sharing).

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

It is considerate and makes the space safer for others. On some platforms like hexbear it is expected. Of course, on many others it is not standard. No real right or wrong, as I see it. I’ve been meaning to change mine to username/username on lemmy because that’s how I would like to be seen and interacted with on this anonymous platform.

How do i figure them out ?

You can always offer yours. Maybe you missed the chance to do that with it being awkward. Most people I know consider it polite to ask something along the lines of “how do you like to be referred to?” Although this has largely been shortened to “what are your pronouns?” The issue in my experience here isn’t asking someone who is comfortable with these discussions (regardless of how they identify), the issue that really pops up is when you ask an innocent question to someone who gets upset by the concept of self-identity. Then they attack you and make you wish you had kept your mouth shut, even though the truth is you were being considerate. Some people also use they/them when in doubt as a relatively safe fallback.

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

No, not unless it is someone who gets upset at the concept of self-identity. Otherwise - how could you?

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

These are third-person pronouns, so in a brief interaction with a stranger you wouldn’t be using these pronouns to their face. You’d say ‘you/your.’ If you’re going to have a longer relationship with an individual, it’s good to find a way to clarify before using assumed pronouns too much. Again this is simple when people around you are comfortable with these discussions - “X identifies as ‘he,’ right? Okay, yeah, so yesterday he…” If you accidentally misgender someone and they point it out, they will generally be awkward in doing so. This doesn’t necessarily mean you’ve upset them, it’s just an awkward thing. If you’re humble about it and fix your gendering then, for most people in most cases, no foul has been committed.

Is it an actual thing or is it currently being pushed to make the world a more inclusive place?

It’s not super common, especially outside of intimate social circles. However there are certainly a number of people who identify preferably as ‘they/them’ as opposed to either he or her. In my experience these people are thoroughly used to being referred to with different pronouns and feel appreciated in the rare event that someone takes the time and effort to use their preferred pronouns.