The imperfect provides the description of the scenario: external conditions such as time, date, weather, etc.
1-Il était midi, il faisait beau , je déjeunais à la terrasse d'un café
It was noon , the weather was nice, I was having lunch at outdoor " café"
The imperfect is used to describe what the character was doing when something happened
2-je déjeunais à la terrasse d'un café en lisant un magazine
nice, I was having lunch at outdoor " café reading a magazine"
The imperfect is used to describe a character's appearance in the story
4-C'était une femme âgée, elle avait des cheveux blancs et une robe bleue.
She was an older lady with white hair and a blue dress
The imperfect is used to describe a physical a mental condition or a state of mind
7-La vieille dame tremblait , elle était choquée, elle ne pouvait pas parler.
The older lady was in a state of chock, she was shaking , she could not talk
The passé composé provides the actions that develop the story line. These actions must have been completed in the past and be specific. It answers to the questions "What happened". The passé composé make the action go forward.
3-Soudain j'ai entendu un cri, je me suis retournée et j'ai vu une femme
All of a sudden I heard a scream, I turned around and I saw a lady
5-Elle a commencé à crier au secours au secours, on m'a volé mon sac
She started to yell, help help , someone stole
6- La police est arrivée et a pris la description du voleur
The police arrived and wrote down the description of the thief
Imperfect and passé composé are also often used together when an action in progress is interrupted by another action . The imperfect is used to describe the action in progress and the passé composé to describe the action that interrupts the action in progress.
Hoisissez la bonne phrase
1-When she arrived he was still in his pajamas a-elle arrivait
b-elle est arrivée
2-When I heard the news, I couldn't speak
3-When I arrived in Paris, I didn't know anybody
4- I was leaving when she arrived a-je suis parti
5-When I met her she worked for Peugeot a-elle a travaillé
6-she was walking down the street when this guy started following her
7-After the accident, I was crying
8-When he told me that I was not listening
a-je n'écoutais pas
b-Je n'ai pas écouté