Study this example situation:

Dennis stopped smoking two years ago. He doesn't smoke any more. But he used to smoke. He used to smoke 40 cigarettes a day. 'He used to smoke' = he smoked regularly for some time in the past, but he doesn't smoke now. He was a smoker, but now he isn't.

'Something used to happen' = something happened regularly in the past but no longer happens;

• I used to play tennis a lot but I don't play very often now.
• Diane used to travel a lot. These days she doesn't go away so often.
• 'Do you go to the cinema very often?' 'Not now, but I used to.' (= I used to go...)

We also use used to... for something that was true but is not true any more:

• This building is now a furniture shop. It used to be a cinema.
• I used to think he was unfriendly but now I realise he's a very nice person.
• I've started drinking coffee recently. I never used to like it before.
• Janet used to have very long hair when she was a child.

'I used to do something' is past. There is no present form. You cannot say 'I use to do'. To talk about the present, use the present simple (I do).

Compare:

• We used to live in a small village but now we live in London.
• here used to be four cinemas in the town. Now there is only one.

The normal question form is did (you) use to...?:

• Did you use to eat a lot of sweets when you were a child? The negative form is didn't use to... . (used not to... is also possible)
• I didn't use to like him. (or I used not to like him.)

Compare I used to do and I was doing (see Unit 6):

• I used to watch TV a lot. (= I watched TV regularly in the past, but I no longer do this)
• I was watching TV when the phone rang. (= I was in the middle of watching TV)

Do not confuse I used to do and I am used to doing (see Unit 60). The structures and meanings are different:

• I used to live alone. (= I lived alone in the past but I no longer live alone)
• I am used to living alone. (= I live alone and I don't find it strange or new because I've been living alone for some time)