Learn Hardcore Korean: hakgyo dwie gongwoni isseoyo. - There is a park behind the school.

In Korean, to indicate a static location you attach the location particle 에 to a noun. 뒤 by itself means “back” or “behind” in a conceptual sense, but it needs 에 to mark it as the place where something exists. So 뒤에 means “at/in the back (of) ….”

What role does 에 play in 뒤에?

The particle 에 has several uses; one of them is to mark the place where someone or something exists. Here, 뒤에 tells us where the park exists—namely, behind the school.

Why is 공원 followed by the subject marker 이 (as in 공원이 있어요)?

Existential sentences in Korean use Noun + 이/가 + 있다/없다 to mean “there is/there isn’t N.” The park (공원) is the thing whose existence is being stated, so it takes the subject marker 이.

What does 있어요 mean here? How is it related to 있다?

있다 is the dictionary form of the verb meaning “to exist” or “to have.” 있어요 is its polite present-tense form. So 공원이 있어요 literally means “A park exists.” In natural English we say, “There is a park.”

Could I drop the subject marker and say 학교 뒤에 공원 있어요?

In casual speech, Koreans often drop particles, especially in spoken or text-message style:

학교 뒤에 공원 있어요 (still polite but slightly clipped)
학교 뒤에 공원 있어 (informal)
However, in standard polite or written Korean, it’s better to keep 이/가 for clarity.

How would I say “There isn’t a park behind the school”?

Just replace 있어요 with its opposite 없어요 (there isn’t):
학교 뒤에 공원이 없어요.

What’s the difference between 뒤에, 뒤, and 뒤쪽에?

뒤: the noun “back” or “rear” (you usually need a particle to show function).
뒤에 (뒤 + 에): “at the back of” – precise static location.
뒤쪽에: “on the back side” or “in the back area” – a bit more approximate or general than 뒤에.

Can I switch 학교 뒤에 and 공원이 (e.g. 공원이 학교 뒤에 있어요)?

Yes. Korean word order is relatively flexible. By putting 공원이 first, you emphasize the park (“As for the park, it’s behind the school”). The basic meaning (“There’s a park behind the school”) stays the same.