Ma’am and sir
The US is a huge country with a ton of different traditions. In some parts of the country, usually in the southern states, calling women “ma’am” and men “sir” is polite. In other parts, it’s not very commonly used, except for in commercial establishments. And even then, calling people (around your age or younger) “man” or “dude” isn’t out of the ordinary.
It’s about showing respect to your elders. I’m sure different countries have different ways of showing respect to others, even if they’re in your age group. I don’t really understand why this would be foreign to anybody, unless their own customs don’t have a formal way of speaking to others.