Learn Turkish: Plastik şişeler yerine cam veya metal şişeler kullanırlar. - They use glass or metal bottles instead of plastic bottles.

yerine means "instead of". While it often requires the noun before it to have a genitive (possessive) ending, here plastik şişeler is a general, non-specific category ("plastic bottles" in general). Because it is non-specific, it stays in its plain form before yerine.

Does yerine have a literal meaning?

Yes! It is made of yer (place) + -i (its) + -n- (buffer letter) + -e (direction marker "to"). So it literally means "to its place." Saying plastik şişeler yerine is like saying "to the place of plastic bottles."

Why don't the words plastik, cam, and metal get plural endings?

When a material (like plastic, glass, or metal) describes an object, it acts like an adjective. In Turkish, adjectives never take plural endings, even if the noun they describe is plural. That is why we say plastik şişeler and not plastikler şişeler.

What tense is being used in kullanırlar?

This is the aorist (simple present) tense, which is used for general statements, habits, and facts. The root is kullan- (use), -ır is the aorist tense marker, and -lar is the "they" ending. It shows that they generally use these bottles, rather than just doing it right now.