Hello! From what I know from my Korean learning is that you show respect by using formal Korean using 씨 after their name if you don't know them that well and are older than you. Also use 저 (cho) to refer to your self formally and always end with 요 (yo) . An example would be when greeting them, say 안녕하세요 (an nyong ha sae yo) ' To people younger than you (that you know) they are your 덩생 (dong saeng) which means younger sibling. You can speak to them informally using 나 (na), 나는 (na neun) , etc. With the same word to greet them, you can say 안녕 (an nyong). You should always bow, to elders, and to people who you are undamiar with.