Does any know how getting marry to an international / foreign person work like?

I’m just a little curious if it works the same or different since my friend’s bf doesn’t live here and he isn’t born here. He’s not a citizen basically but they wanna get marry.

She still live under her parent’s roof and her bf live in a house with his roomies. Do they have to have their own place to be able to get marry? They’re financially stable but obviously can’t get a house anytime soon and they’re not planning to have kids, yet, but want to get marry?

I know it’s not my business to bother but I don’t feel like asking her and bugging her but I just wanna know how it’ll work out for them. And ofc, just in general with foreign as wellzzz 😁

Update: California