Though it's really tough for you English speakers to learn grammatical gender in another language, it's really hard for we speakers of other languages to pick up the "a" and "the."
We must remember that the "a" and "an" go in front of nouns that we're not clear which one is being talked about. For example, - an apple on the table, or a pen on the desk. We don't have a clue what apple or what pen is being talked about.
But if the speaker said this - I see the dog in the street.
Or someone said, The tiny cat sat on the rug, or the black dog in the street. Then we know what cat and dog is being talked about. It's definitely "not a walk in the park" to learn a new language, but it can be done.