Expressing obligation in English is normally expressed with the use of have to, must, should or ought. This is usually done thorugh the pattern infinitive form of the verb+야 (ya) plus the verb 해요 (haeyo) or 돼요 (dweyo). 야 stands for only if so literally the pattern I provided means only if [someone] will do or become <verb>. However in the Korean context its just a simple way of saying someone is compelled or has to do something.
- 내일 친구를 만나야 해요. (Naeil chingureul mannaya haeyo). I need to meet a friend tomorrow.
의사의 충고로 많이 물을 마셔야 해요. (Ouisa chunggoro mureul masyeoya haeyo). I need to drink plenty of water through doctor’s advice.
도서관 안에서는 조용히 해야 돼요. (Doseogwan aneseonun choyonghi haeyoya dwaeyo) You have to be quiet inside the library.
There are other verbs which can be used in combination with infinitive verb + 야 like the following examples below:
돈이 있어야 들어가요. (Doni isseoya deurogayo) You need money to get in.
사장한테 물어봐야 알겠어요. (Sajanghante mureobwaya algesseoyo). We will be able to understand by asking the boss.