"I eat apples" is correct. In English, you need an article before singular nouns. For example, "I eat an apple" or "I eat the apple". You cannot merely write "I eat apple" when the noun is singular. However you don't need the article with plural nouns. So you can write "I eat apples" or "I eat the apples". The difference is if you want to specify the apples or talk about a more general situation.

I eat an apple (singular) I eat many apples (plural) hope this helps