Ben elma yerim.
English: I eat (an) apple(s).
The 'belirtisiz nesne' in Turkish is the 'indefinite object' in a sentence. It is used when you talk about something in general, not a specific thing.
Use the belirtisiz nesne when you are talking about something in a general or non-specific way. If you do not mean a particular object, but any object of that type, you use this form.
Ben elma yerim.
English: I eat (an) apple(s).
Ayşe kitap okuyor.
English: Ayşe is reading (a) book(s).
Ali film izler.
English: Ali watches (a) film(s).
Çocuklar oyun oynar.
English: Children play (a) game/games.