Learn Farsi: این در و آن پنجره خیلی کثیف است. - This door and that window are very dirty.

Just like in English, Farsi demonstratives are placed directly before the noun they point to. So you say این در (this door) and آن پنجره (that window).

The English translation says 'are', but the sentence ends with است (is). Why is a singular verb used for two things?

This is a special rule in Farsi: if the subject of the sentence consists of inanimate objects (things that aren't alive, like doors and windows), the verb is usually singular. Even though 'this door and that window' adds up to a plural subject, you use the singular است (is) instead of a plural verb.

Where do describing words like خیلی کثیف (very dirty) go in a Farsi sentence?

Because Farsi strongly prefers putting the verb at the very end of the sentence, adjectives that describe the state of the subject go right before the verb. The literal word order here is 'This door and that window very dirty is.'

How should I pronounce the word و (and) in the middle of this sentence?

Although it is formally pronounced 'va', in everyday spoken Farsi it becomes a quick 'o' sound that links to the previous word. You will usually hear native speakers say 'in dar-o ân panjare'.