first of all welcome i love asian culture! to answer your questions this platform is a bit different and i think @uwelang pretty much covered the theme, what i want to say is that at least for now steemin is an open minded community and what i mean by that is that you dont have to worry about everyone judging what you say and ofc there are no trolls!
About private messages again @uwelang nailed it and a guide for you except what mentioned could be https://steemit.com/steemit/@shenanigator/updated-steemit-faq-section-posting ( he has other posts as well you can find them easily)

Try to have as much fun as you can enjoy it, interact with new people( i believe that would be great for everyone) and share your stories
( teach us korean :P )