Learn Hardcore Turkish: Eğer her saniyeyi verimli kullanırsan, boşa geçen vakit azalır. - If you make efficient use of every second, wasted time decreases.

The suffix -rsan marks the 2nd person singular conditional (“if you …”) in Turkish. You take the aorist stem of the verb kullan- (to use), add the conditional marker -ır/-ir (depending on vowel harmony), and then the personal ending -sın (you). Vowel harmony changes -ır + sın → -ırsın, and in fast speech the -sın often loses its vowel to become -rsan. So kullanırsan = “if you use.”

Why is her saniyeyi in the accusative case (with -yi) rather than the nominative?

In Turkish, definite direct objects take the accusative suffix. Her saniye (“every second”) is the thing being used, so it’s a definite object. You add -yi (or -yı/-yu/-yü by vowel harmony) to mark it as her saniyeyi (“every second” as a specific chunk of time), indicating it’s the direct object of kullanırsan.

What is boşa geçen in boşa geçen vakit, and why use geçen?

Boşa geçen is a participle phrase modifying vakit (“time”).

boşa: in vain, wasted
geçen: the present participle of geçmek (“to pass”)
Together boşa geçen = “that passes in vain,” so boşa geçen vakit means “time that goes to waste” or simply “wasted time.”

Why is vakit used here instead of zaman?

Both vakit and zaman can mean “time,” but they have subtle differences in usage and collocation.

vakit often refers to a span or portion of time (e.g. boşa geçen vakit, geç vakit).
zaman is more abstract or general (e.g. zaman geçiyor = “time is passing”).
Here Turkish speakers prefer vakit when talking about “wasted time” as a measurable chunk.

What role does verimli play, and how would you translate it?

Verimli is an adjective meaning “efficient” or “productive.” It describes kullanmak (“to use”), so verimli kullanmak means “to use (something) efficiently” or “to make productive use of (something).”

Why is there no subject like sen (you) in the sentence?

Turkish is a pro-drop language: subject pronouns are often omitted because the verb ending already shows person and number. Here -rsan on kullanırsan tells you the subject is “you,” so you don’t need to say sen again.

How is word order working in this sentence?

Turkish generally follows SOV (subject-object-verb) order. This sentence is conditional, so the clause order is:
1) Eğer (if) + condition clause (her saniyeyi verimli kullanırsan)
2) main clause (boşa geçen vakit azalır)
Within each clause you see object (her saniyeyi, boşa geçen vakit) before the verb (kullanırsan, azalır).

What does azalır derive from, and what tense/mood is it?

Azalır comes from the verb azalmak (“to decrease”). Here it’s in the simple present tense, which often expresses general truths or habitual actions in Turkish. So azalır = “(it) decreases” or “will decrease” in the sense of a natural, expected outcome.