Vocabulary: Promise

You probably heard of this word in many songs and drama, 약속 (yaksok).  This word means promise.  It also means appointment or undertaking.

약속 (yaksok) - promise

So if you want to say I promise you can say 약속해요 (yaksokhaeyo).  Now if you want to ask someone to make a promise you can say 약속하세요 (yaksokhaseyo).