Thank you Hoon ^^

er usually when you ask something. you put '니까?' 'ni kka and it's polite way to ask... 오늘 언제 옵니까? and means (when are you coming today?) cf) 오늘 언제 오니? (when are you coming today?) informal way to say(to your friend or younger one) 저건 무엇입니까? what is it?(polite way to say) 저건 뭐니? what is it?(informal way to say) cf) it's different usage of '니까' when you said something already and emphasis again it 간다니까! (i told you i'm going!!!)