Choose does when the subject is one person or thing, the way he, she, or it would be. Choose do when the subject is I, you, we, or they. The main verb always stays in its base form, so does work, never does works.
Asking a question about someone else: use Does. Does my sister work here? The short answer is She doesn't. If you want more detail, ask Where does he work?
Asking about yourself or a group: use Do. Why do they leave early? The short answer is I don't.
Saying something is not true: use doesn't for one person or thing (he, she, it) and don't for I, you, we, they. Compare He doesn't work here with They don't work here.
Watch the verb after does. Because does already carries the third-person s, the main verb loses its own s and returns to the base form: Does she work here is right, never Does she works. The same applies to one as a subject, since one person or thing counts as he, she, or it: Does one bus go downtown?