In English yes/no questions, the auxiliary verb moves to the front before the subject, reversing their normal order. "You are going" becomes "Are you going?"; "They have finished" becomes "Have they finished?". When there is no auxiliary verb, "do" or "does" is added and inverted: "You like pizza?" becomes "Do you like pizza?".
Identify the auxiliary verb in a statement and move it to the front. If there's no auxiliary (simple present or simple past with no helping verb), add "do," "does," or "did" and invert it to the front.
English declarative sentences follow a Subject-Verb-Object order: "You *are* going." "They *have* finished." The verb phrase anchors in the middle, after the subject. When you form a yes/no question, English moves the first auxiliary verb to a position *before* the subject — a process called subject-auxiliary inversion. The subject and auxiliary swap positions: "Are *you* going?" "Have *they* finished?" The rest of the verb phrase stays in place; only the auxiliary moves.
You know from your study of auxiliary verbs that they include *be*, *have*, *do*, *will*, *would*, *can*, *could*, *shall*, *should*, *may*, *might*, and *must*. These are the verbs that actually move in inversion. The main verb does not move — a common error is to move the wrong verb. "Going are you?" moves the participle, not the auxiliary; "Are you going?" correctly moves *are* while leaving *going* in place.
The harder case is when there is no auxiliary at all — the simple present and simple past tenses in their affirmative form. "She *likes* coffee." "He *went* home." There is no auxiliary here to invert. English solves this with do-support: a dummy auxiliary *do* (or *does* for third-person singular, *did* for past) is inserted into the structure and then inverted to the front. "Does she like coffee?" "Did he go home?" The main verb simultaneously shifts from its inflected form (*likes* → *like*, *went* → *go*) because *do* is now carrying the tense. Notice that you never say "Does she likes coffee?" — the tense marking moves to *does*, leaving the main verb in its base form.
These two mechanisms — direct inversion of an existing auxiliary, and do-support when there is none — cover all yes/no questions in English. They also apply in negative questions, tag questions, and many conditional constructions. The underlying principle is consistent: English marks questions by moving an auxiliary verb to a position before the subject. Once you see this as a single rule with a predictable exception (do-support), the pattern becomes reliable rather than a list of cases to memorize.