Affirmative Form: subject + used to / would + infinitive
Negative Form: subject + did not + use to + infinitive
Question Form: did … use to + infinitive?
Examples:
She used to / would lock the door.
I didn’t use to lock the door.
Did they use to lock the door?
Used to / Would is used:
To talk about past repeated actions:
She would leave the door unlocked whenever she was at home.
Negative “Would” is uncommon.
To describe permanent situations that are no longer true.
Bill Murphy used to work for the police, but he doesn’t now.Note that “Not used to” is not used when discussing duration:
Bill Murphy worked for the police force for over 17 years.