I used to …

Dave used to work in a factory. Now he works in a supermarket.

Dave used to work in a factory = he worked in a factory before, but he doesn’t work there now:

When I was a child, I used to like chocolate.
I used to read a lot of books, but I don’t read much these days.
Liz has got short hair now, but it used to be very long.
They used to live in the same street as us, so we used to see them a lot. But we don’t see them very often these days.
Helen used to have a piano, but she sold it a few years ago.

The negative is I didn’t use to …

When I was a child, I didn’t use to like tomatoes.

The question is did you use to … ?

Where did you use to live before you came here?

We use used to … only for the past. You cannot say ‘I use to … ‘ for the present:

I used to play tennis. These days I play golf. (not I use to play golf )
We usually get up early. (not We use to get up early)