In Korean, there are too many versions of "because" for me to count today. However, 때문에 is the best generic one to choose when you aren't sure. Here are the important things to know about it:
1. It can be used like, "때문에" like English speakers might say, "Just because". It's equally informal and potentially impolite.
2. It is often used to end a sentence even though it's not supposed to. "학교 때문에요". Just randomly add "요" to make it sound more polite.
3. Korean sentence logic goes like this:
First: The cause 학교에 나는 늦게 오기 때문에
Second: The effect 선생님이 화가 나요.
학교에 나는 늦게 오기 때문에 선생님이 화가 나요.
4. It can be used with past tense ㅆ like 왔기 때문에.