Learn Hardcore Turkish: Saç çok uzun.

In Turkish, present-tense nominal sentences drop the copula (to be). The state is understood without an explicit verb. Formally, you might see Saç çok uzundur (using the suffix -dur), but in everyday speech the -dur ending is omitted.

Why doesn't saç have any suffix?

Here saç is the subject in the nominative case. Turkish subjects are typically unmarked (no case ending or article) in simple predicative sentences.

Why does uzun come after saç, when in English adjectives usually come before nouns?

When you use an adjective attributively (to directly modify a noun), in Turkish it precedes the noun: uzun saç = long hair. But in a predicative clause (making a statement), the usual order is Subject + Adverb + Adjective, so Saç uzun = the hair is long.

How would I say my hair is very long in Turkish?

Attach the first-person possessive suffix -ım to saç: Saçım çok uzun. To be more explicit, you can add the possessive pronoun: Benim saçım çok uzun.

Can I use saçlar instead of saç in this sentence?

Generally saç is uncountable and is used in the singular to talk about hair collectively. saçlar (literally “hairs”) refers to individual strands or is used in some idiomatic expressions, but for describing the length of someone’s hair, the singular saç is standard.

Why doesn't uzun carry any suffix (like case or agreement)?

Turkish adjectives are invariable: they don't inflect for case, number, or person. Whether attributive or predicative, adjectives remain in their base form (uzun) and only their position relative to the noun/adverb indicates their function.