We use 'used to' to talk about a habit or a situation that existed in the past.
- I used to smoke. (= Now I don't smoke.)
- She used to be rich. (= She is not rich now.)
- There used to be a house here. (= The house is not here now.)
Put 'used to' before a verb in the plain form: used to + verb. For example: 'used to + cook', 'used to + travel'.
To negate 'used to', put 'didn’t' in front of it, and remove "d" : didn't use to.
- I didn’t use to smoke. (= I smoke now)
- I never used to smoke. (= I smoke now)
- She didn’t use to be rich. (= She is rich now)
- There didn’t use to be a house here. (= Now there is a house here)
Tip: "Didn't Used to" vs "Didn't Use to"
You will see both "didn't use to" and "didn't used to" in major English-language publications. On exams however, you may want to use "didn't use to" to be safe.