When do you use imparfait instead of passé composé to describe past events?

While the passé composé is used to refer to specific past events of interest, the imparfait can loosely be thought of as describing “background information” such as:

- States of being and habitual actions:

“Quand j’était petit, je jouais le piano.”

- Actions of an unspecified duration. Descriptions of time, weather and feelings:

“Il faisait beau. Tout les oiseaux chantaient. Elle était très belle. Il l'aimait.”

- Actions that are in progress when a sudden event occurs:

“Je dormais quand le téléphone a sonné.”