"He eats apples."
Translation:Dia makan apel.
Dia refers to a person (He/She). Ia refers to non-human (Animals/Objects etc). To refer Dia as a person is considered rude.
In Standard Malay, dia is almost exclusively used as a pronoun for living beings while ia is mainly for non living things--although the latter can be used for both. In Standard Indonesian dia is synonymous with ia, but the latter is much less common, and ia is not used as a pronoun (we use noun+determiner instead).
In daily speech, ia is almost nonexistent.