Learn Turkish: İşçiler yeni ürünü üretince mühendis onu kontrol ediyor. - As soon as the workers produce the new product, the engineer checks it.

It uses the suffix -ince attached to the verb root üret- (to produce). This suffix (which follows vowel harmony as -ince, -ınca, -unca, or -ünce) connects two actions, meaning "when" or "as soon as". Notice that üretince doesn't have a tense or person marker of its own; it relies on the main verb (ediyor) to show when the action happens.

Why does ürün have an extra -ü at the end of yeni ürünü?

The extra -ü is the definite accusative (direct object) case marker. Because the workers are producing a specific item ("the" new product), it needs this ending to show it directly receives the action of the verb üretince.

Where does the n come from in onu?

Onu means "it" as a direct object, referring back to the product. The root is the pronoun o (it), and the case marker is -u. When adding a vowel suffix to the pronouns o, bu, or şu, Turkish uses -n- as a buffer letter instead of the usual -y-, making it o-n-u.

The dictionary verb is kontrol etmek. Why does it change to kontrol ediyor?