Learn Hardcore Turkish: Antep fıstığı tuzlu.

In Turkish, the present‐tense copula (to be) is normally omitted in sentences with noun or adjective predicates. So Antep fıstığı tuzlu literally reads as Antep pistachio (is) salty without a separate word for is.

Why does tuzlu come after Antep fıstığı, while in English we say “salty pistachio”?

Because tuzlu here is a predicate adjective, not an attributive one. Turkish follows a Subject–Predicate order, so you say
Subject: Antep fıstığı
Predicate adjective: tuzlu
If you actually want “salty pistachio” as an adjective before the noun, you’d write tuzlu Antep fıstığı.

What does the -ı in fıstığı do?

That -ı is the third-person singular possessive suffix. In the compound Antep fıstığı, it marks fıstık (“pistachio”) as “of Antep.” This is a common pattern in place–product compounds (e.g. Bursa kestanesi = “Bursa’s chestnut”).

How is the adjective tuzlu formed from the noun tuz?

Tuz means “salt.” Adding the suffix -lu (one of -lı/-li/-lü, chosen by vowel harmony) turns nouns into adjectives meaning “having or full of X.”
tuz + lu → tuzlu (“salty”)

How would I make the sentence negative?