It is generally correct to say that whenever there is no form of BE (both as a full/lexical verb and an auxiliary verb) or HAVE (as an auxiliary) or a modal verb, and you want to construct a question or negative form, you need the auxiliary verb DO; and that whenever these forms are used, DO is not.
It is simpler to say that we use the auxiliary verb DO to construct the question and negative forms of the present and past simple tenses of all full/lexical verbs except BE.
Or: The negative and interrogative forms of all full/lexical verbs (except BE) require an auxiliary verb. If no other auxiliary is present, then we use DO.
We can use DO for the emphatic imperative of BE: Do be careful
We must use DO for the negative imperative of BE and HAVE: Don't be silly. Don't have too much to eat.
Some speakers of BrE do not use the auxiliary DO with the full verb HAVE: Have you a moment? I haven't a clue.
- For Teachers