In general, you use the imperfect to:
Describe past habits:
Quando ero piccola, andavo sempre in vacanza al mare.
When I was little, I used to always go to the beach for vacation.
Describe characteristics of people or of places in the past:
La mia mamma da giovane era magra e sportiva, aveva lunghi capelli neri.
When my mom was young, she was thin and athletic, and she had long black hair.
Describe emotions and perceptions in the past:
Ieri ero triste perché è partito il mio ragazzo.
I was sad yesterday because my boyfriend left.
Ieri avevo mal di denti.
Yesterday I had a toothache.
Describe simultaneous actions in the past.
Mentre studiavo, Gianni ascoltava Mozart.
While I was studying, Gianni was listening to Mozart.
Describe weather and time-of-day in the past:
Ieri faceva molto caldo.
Yesterday it was very hot.
Erano le dieci; era mezzanotte
It was ten o’clock; it was midnight
Describe someone’s age in the past
Nel 1967 mio padre aveva 15 anni
In 1967 my father was 15.