THE BIG PICTURE: Use used + infinitive of verb to discuss past situations, conditions or habits which are now different or finished.
Stella used to live in Brooklyn, but now she lives in Manhattan.
David used to cook dinner every night, but now he gets take-out several times a week.
Our mailman used to come at 11AM every day, but now he comes later.
Note that in conversational American English, you will hear “used to” pronounced “useta”.
To form questions and negatives with “used to,” use “do.”
Did you use to play tennis every Saturday?
Mary didn’t use to believe in ghosts.