Affirmative: You speak Spanish.
Question: Do you speak Spanish?
You will see that we add DO at the beginning of the affirmative
sentence to make it a question. We use Do when the subject is I,
you, we or they.
Affirmative: He speaks Spanish.
Question: Does he speak Spanish?
When the subject is he, she or it, we add DOES at
the beginning to make the affirmative sentence a question. Notice that the
letter S at the end of the verb in the affirmative sentence (because it
is in third person) disappears in the question. We will see the reason why below.
We DON'T use Do or Does in questions that have the verb
To Be or Modal Verbs (can, must, might, should etc.)