USE
1. USED TO and regular actions in the past (that do not happen now)
We use "used to" to talk about something that happened regularly in the past but does not happen now.
I used to play chess every day.
(I played chess every day for some time in the past but I don't play chess every day now.)
I didn't use to play computer games every day.
(I didn't play computer games every day for some time in the past but I play computer games every day now.)
2. USED TO and something that was true in the past (and is not true now)
We use "used to" to talk about something that was true in the past but is not true any more.
I used to have short hair.
(I had short hair in the past but now I have long hair. My hair is not short any more.)
This building used to be a cinema. Now it is a furniture shop.
(Some time ago the building was a cinema. It is not a cinema any more. It is a furniture shop now.)
Sam used to think that Ann was unfriendly but now he realises that she is a very nice girl.
(Sam thought that Ann wasn't friendly but he doesn't think so any more. Now he thinks that she is nice.)
3. USED TO or BE USED TO / GET USED TO"
Do not confuse "used to" and "be/get used to".
We use "get used to" to talk about something you became familiar with.
Compare:
I used to live in a big city.
(I lived in a big city for some time in the past but I do not live in a big city any more. I live in a small town now.)
I am used to living in a big city.
(I am familiar with living in a big city. I am accustomed to living in a big city. I do not find it new, strange or difficult.)
I got used to living in a big city.
(I became familiar with living in a big city. It is not new, strange or difficult any more.)