I know the rule of definite and indefinite articles ( A, An ), but I see lots of people who speak English as their native mother language and they write a sentences like this : "I like a apple." should not that be "I like an apple ?." this really confuses me
It is entirely possible that some native speakers would write (write?)
I like a apple.
though I've never seen it written this way, and you are correct in thinking the article should be
I like an apple.
but actually, the correct sentence would be
I would like an apple.
When spoken, what might be said is
I wanna apple.
depending on dialect, but what is not said is
I wannan apple.