Learn Hardcore Turkish: Yirmi kitap masada duruyor.

In Turkish, when you use a numeral like yirmi, the counted noun stays in its singular form. You do not add the plural suffix -lar/-ler. So you say yirmi kitap (twenty book) rather than yirmi kitaplar.

What does masada mean?

Masada is the noun masa (table) plus the locative case suffix -da (with vowel harmony). It means on the table or at the table.

What is the function of the verb duruyor here?

Duruyor is the present continuous form of durmak, which literally means “to stand” or “to stop.” In this context it expresses a static location or state. So Yirmi kitap masada duruyor conveys that the books are located (literally “are standing”) on the table.

Could we use var instead of duruyor?

Yes. Masada yirmi kitap var also means “There are twenty books on the table.” The nuance is:

var purely states existence.
duruyor adds a sense of the items being stationary or “standing” at that spot.

Why is the word order Yirmi kitap masada duruyor? Can we switch it?