Something happened regularly or habitually in the past
would (for actions)My granny was wonderful. Each time we stayed at her place, she would hide treats under our pillows.
used to (for actions and situations)
As a teenager I used to walk to my friends, nowadays I always go by car.
There used to be an old hospital here, but it has been replaced by a new one.
As a kitten she used to be very naughty, but now she is a sweet, old cat.