Learn Farsi: بیست کتاب جدید در قفسه است. - There are twenty new books on the shelf.

In Farsi, any noun that comes right after a number is always kept in its singular form. You never make the noun plural if you have already stated the exact quantity. So, "twenty books" is literally "twenty book" (بیست کتاب).

Why is the verb at the end است (is) instead of a plural verb like "are"?

In Farsi grammar, inanimate objects (things that aren't humans or animals) usually take a singular verb, even if there is more than one of them. Since books are inanimate, the sentence uses the singular است ("is") instead of the plural هستند ("are").

I don't see a word for "there" in this sentence. How do we get "There are twenty new books"?

Farsi doesn't use a filler word like "there" to state that something exists somewhere. You simply put the subject first, then the location, and finally the verb. The literal translation is "Twenty new book in shelf is", which naturally means "There are twenty new books on the shelf" in English.

I know the word در means "in". Why does the English translation say "on the shelf"?

Prepositions don't always match perfectly between Farsi and English. While در usually translates to "in", it is the natural preposition Farsi speakers use with قفسه (shelf). You can think of it as the books being located "within" the shelving unit.