If I may explain something, just based on the level of Korean indicated in your profile. What the other answers are telling you is correct, but in order to understand it, you have to understand the concept of Korean Grammar Patterns or 문법. This was a big obstacle when I was first learning Korean, and it stayed that way for a long time because nobody really explained the concept to me. So let me attempt it for you so you don't have the same long period of frustration. In English, we often have words for expressions that are given in 'grammar patterns' (the English term I have in a couple of textbooks). In Korean, this is called 분법 which is also translated as "grammar," but when you study 문법, it is more than just the grammar concepts that we have in English. You most commonly (but not always) hear the grammar patterns at the end of the sentence in Korean, and they change the meaning of the sentence from what it would be if the sentence just ended with the verb as you might expect from the first days of learning Korean. What the other answers are giving you is the grammar pattern that is used to express something that must be done. In this case, the 여야 한다 or 야 한다 or 여야 댄다 or 야 된다 that is being used in the examples is what indicates "must be done," or "you must." Just to further illustrate the concept, the example given above, "ㄴ다고" is what marks reported speech, but it is used in conjunction with "하다" for speech, or "생각하다" for reporting a thought. So the combined "~야한다고 샏각한다" means "Think you must do ~" or "Think ~ must be done." Much of Korean study will involve 문법, so if you hadn't gotten that concept to be able to recognize it and re--use it, I hope that explanation helps. I sure wish someone had given it to me much earlier.

must (verb inf.) -- (동사 -아/어/여 표현)야 하다. to be obligated to (verb inf.) -- (동사 -아/어/여 표현)야 되다. to think that + (verb) -- (동사 어간 + -ㄴ/는다)고 생각하다. to think that + (adj.) -- (현용사 어간 + -다)고 생각하다. Thus, "I think that you must learn korean." = 나는 네가 한국말을 배운다고 생각한다. (N.B. 한다 [-ㄴ/는다] is an expression of causal writing form for plain display of an incident.)

Must learn : 배워야한다 I think you must learn korean 난 네가 한국말 배워야한다고 생각한다