I will try not to make a complicated grammar explanation. "DO" is a major auxiliary for the Present Simple tense.
The present for "BE" = am, are, is .
In the present simple, "BE" is used to link a subject to a detail about the subject. Here are some examples:
She is Sarah. (Name)
She is pretty. (adjective)
He is late. (adjective)
They are very nice (an adjective with "very" describing it.)
He is in Africa.
They are at home.
We are hungry.
He is a teacher.
They are doctors.
He is French.
"DO" is an auxiliary, or helping verb in the question you are asking ("DO" can also be a normal verb).
Auxiliary "DO" always wants to be helping another verb (except in short answers like "Yes, I do".), and usually appears in Present Simple questions and negative sentences. Present Simple "DO" = do, does.
You can tell if you are using auxiliary "DO" correctly if it is helping another verb in the sentence. Examples:
Do you like opera?
Does he want a car?
I don't wear bracelets.
Don't do that. (In this sentence, the subject "you" is assumed, and the bold do is a normal verb. It is possible to have the auxiliary and the normal verb in the same sentence.)
Do you do sports?
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