Learn Farsi: پارک بزرگ پشت بیمارستان است.

They connect using the Ezafe (an invisible "-e" sound). The word posht means "behind", and to link it to the place it is behind, you add the Ezafe. So, it is pronounced posht-e bimârestân. Most spatial words you are learning now, like "under" or "next to", need this connecting sound to link to a noun.

Why is the adjective after the noun in pârk bozorg?

In Farsi, nouns usually come before their adjectives. Just like with location words, we use the Ezafe to link the noun to its describing word. So "the big park" is spoken as pârk-e bozorg. Keep in mind that this connecting "-e" sound is almost never written in the Farsi alphabet, so you have to know it's there!

Where is the word for "the" in pârk-e bozorg and bimârestân?

Farsi doesn't have a separate word for "the". A plain noun can mean "a park" or "the park" depending on the context. Since this sentence is stating a fact about a specific location, it naturally translates to "the big park" and "the hospital" in English.

Why is ast ("is") at the very end of the sentence?

Farsi has a different sentence structure than English. While English puts the verb right after the subject (The park is behind the hospital), Farsi places the main verb at the very end. This is a very common rule: verbs like ast will almost always wait for you at the end of the sentence!