Learn Turkish: Yeni inşaat yarın tamamlanacak. - The new construction will be completed tomorrow.

The base verb is tamamlamak (to complete). Because the root tamamla- ends in a vowel, its passive suffix is just -n, making it tamamlan- (to be completed). Finally, we add the future tense suffix -acak to get tamamlanacak (it will be completed).

Why is the passive suffix just -n here instead of -il or -in?

In Turkish, the passive suffix changes depending on how the verb root ends. If a verb ends in a consonant, it usually takes -il or -ın (like yapmak becoming yapılmak). But if the verb already ends in a vowel, like tamamla-, it takes -n so you avoid having two vowels bump into each other.

Since tamam is the common word for okay, how did it turn into the verb for complete?

The root word tamam originally means complete or finished (which is why it is used as okay or done). By adding the suffix -la, which turns nouns and adjectives into verbs, it becomes tamamlamak (to make complete).

Why is there no personal suffix at the very end of tamamlanacak?