In the present simple, one small split decides everything: when the subject is he, she or it, the question takes does. Everyone else, meaning I, you, we and they, takes do instead. So the person you're asking about, not the person asking, picks the form.
Examples
- Does she work here?
- Do they live nearby?
- Does the bus stop at this corner?
- Do we need tickets?
Notice that after does or do, the main verb stays in its base form, with no -s, no matter who the subject is. The auxiliary carries the third-person marking, so the verb doesn't have to.
Watch out
A common slip is keeping the -s on the verb after does: Does she works here? Since does already shows it's third person singular, the verb drops back to base form: Does she work here? The same happens with doesn't: It doesn't work, not doesn't works.
Short answers follow the subject, not the question's opening word: Yes, she does. No, he doesn't. And for I, you, we and they, the short answers use do and don't: Yes, they do. No, I don't.
For negatives, it's doesn't plus the base verb, no -s: It doesn't work. Short answers repeat does, not the main verb: Yes, she does. No, he doesn't.
Use does when your subject is he, she or it in a present simple question. Does she work here? The main verb stays in its base form, with no -s. With any other subject you switch to do: Do they live nearby?
You're asking about one other person. He, she or it as the subject means does comes first, and the verb drops its -s: Does he play tennis? Not Does he plays, because does already carries the third-person ending.
You're asking about a group, or the person you're talking to, rather than one other person. I, you, we or they take do instead: Do they play tennis? Same word order, different auxiliary. That fuller do-versus-does choice is covered in the do/does article.
You're checking a habit or routine rather than one moment. Does she take the bus to work? fits an everyday fact. For something happening right now you'd use a different tense, so keep does for regular, general situations.
You're writing a negative about him, her or it. The pattern is subject plus doesn't plus the base verb: She doesn't sing. Doesn't is the usual short form of does not, and doesn't takes the ending, so never It doesn't works. Other subjects use don't: They don't sing.
You're answering a does question. The answer repeats does, not the main verb: Does he play tennis? Yes, he does. No, he doesn't.