Used to is used to talk about things that were true in the past, but aren’t anymore.
I used to know him so well.
We used to live in England.
Did you use to go out with Janice?
Also, used to can be used to talk about recurring habits in the past.
I used to play football every week.
She used to drink, but now doesn’t.
Also, the past tense goes on the word do for the negative form: I didn’t use to
I didn’t use to hang out with him. (now I do)
She didn’t use to drink that much. (now she does)
Structure: Used to + infinitive.