#1

to describe events in the past that occured regularly, repeatedly or frequently :

L'année dernière, Sophie allait à la campagne tous les week-end.
(Last year, Sophie used to go to the countryside every weekend.)

#2

for descriptions in the past, e.g. the weather, how things used to be, etc :

Il faisait beau.
(The weather was fine.)

C'était magnifique !
(It was great !)

Autrefois, il n'y avait les automobiles.
(There were no automobiles in the past.)

#3

to describe an event in the past that lasted for a long time :

À cette époque, nous habitions à Chennai.
(At that time, we lived in Chennai.)

also used with « depuis » to express durations of an event in the past :

Nous habitions à Chennai depuis 5 ans.
(We had been living in Chennai for 5 years.)

#4

to describe something one wanted to do but didn't, or to make excuses :

Je voulais finir mes devoirs, mais j'étais fatigué.
(I wanted to finish my homework but I was tired.)

Ce n'était pas de ma faute.
(I wasn't my fault.)

#5

to translate the English expressions "was … … …-ing" or "were … … …-ing" :

Je faisais mes devoirs quand Pierre est venu.
(I was doing my homework when Pierre came.)