The imperfect tense and the passé composé are both past tenses which are used in different situations. The imperfect tense is used in three main cases:Habitual actions-> What used to happen regularly in the past eg. quand j'étais jejune, je jouais au footDescriptions in the past->what was happening in the past eg. il pleuvaitOngoing actions interrupted by a sudden event-> what was going on when something else happened eg. je regardais la télévision quand quelqu'un a sonnéGenerally, the imperfect tense is used to describe a setting: ongoing past events without reference to a time of starting or finishing or with an indefinite time reference. For this reason, it can be imagined as a video recording. Another way to understand whether it should be used is to ask the question: can the action or event be put ion a diary? If not, because we don't know when the event started or ended, then the imperfect is the right tense. The passé composé is instead used to describe a specific action or event in the past:Completed actions in the past with a specific end and start time or time reference eg. hier, j'ai vu ma mèreA plot or a series of events/actions eg. j'ai écrit et puis j'ai téléphonéRepeated one-off events (not habitual) eg. j'ai participé plusieurs fois à des fouillesUnlike the imperfect, the passé composé is used to recount specific events that move the plot forward, so it can be imagined as a snapshot of events. Actions or events in the passé composé have an end and start time so they can be put in a diary.