· In English, questions are normally formed by putting an auxiliary verb before the subject.

Examples:
  Have you been to Holland? (NOT You have been to Holland?)
  Where can I get a taxi? (NOT Where I can get a taxi?)
  Why are you waiting here? (NOT Why you are waiting here?)

· If there is no auxiliary verb, use the verb do.

Examples:
  What do you want? (NOT What you want?)
  What does avoid mean? (NOT What means avoid?)

· The auxiliary verb goes before the subject, not before the verb.

Examples:
  Is your sister making lunch? (NOT Is making your sister lunch?)
  Where are your parents living now? (NOT Where are living your parents now?)

· After the verb do, use the infinitive without to.

Examples:
  Where does he work? (NOT Where does he works?)
  Where did you go yesterday? (NOT Where did you went?)

· Do not use do with other auxiliary verbs or with the verb to be.

Examples:
  Can you speak Spanish? (NOT Do you can speak Spanish?)
  Are you Scottish? (NOT Do you are Scottish?)

· We do not use do when the subject is a question word (who, what, which etc.)

Examples:
  What happened? (NOT What did happen?)
  Who lives in that flat? (NOT Who does live in that flat?)
  Which team won? (NOT Which team did win?)

· Use do if the question word is the object.

Examples:
  What did you do yesterday?
  Where does your brother live?
  What do you usually have for breakfast?