The English grammatical structure "used to" + verb refers to past habits, something that you did regularly or repeatedly in the past but which you no longer do today. This construction only exists in the past tense, there is no present tense for it.
- Thomas used to drink beer. Now he prefers wine.
- Janet used to fly to Paris. Now she takes the Eurostar.
When used negatively or interrogatively, "used to" becomes "use to" because the past tense is already indicated by the auxilliary did:
- I didn't use to drive to work. I always took the subway.
- Did Bob use to live in Wales? Yes, but now he lives in Scotland.
Note that you cannot use this structure to say how often something happened or how long it took.
- Janet used to visit Paris seven times. --> Janet visited Paris seven times.
- Bob used to live in Wales for three years. --> Bob lived in Wales for three years.
Finally, do not to confuse this structure with "to be/get used to" + noun, where "used" means "accustomed" and describes a current state. For example: Now that I live in the city, I am used to the noise and pollution.