"An is at the train station."
Translation:An ở nhà ga.
là should be omitted. You can't be a preposition nor a location. Là means to be something. Tôi là sinh viên means I am a student. "Tôi là ở nhà" would mean "I am a am at home", instead of "I am at home". "là" should be omitted. ở would already mean to be at. Vietnamese grammar is more simplified than English. "I at home" is enough to get the point across. Occasionally other words are used to make note of time (currently, previously, will) but usually basic phrases like this are used