These are some simple functions that help you get user information:
qa_db_user_account_selectspec() qa_db_user_profile_selectspec() qa_db_userfields_selectspec()
Although most likely you'll be only interested in the second one. You can see them in action here.
Just follow the three variables assigned for each of those functions in that link ($useraccount, $userprofile, $userfields) and you'll have the tutorial right there :)
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