When would you use the imperfect tense, and how do you construct it?

It is used when:-Talking about something that used to happen, i.e. was ongoing for a period of time-The weather in the past-Physical description of something in the past-Talking about something that was happening when something else happened during it, e.g. you would translate "I was playing football when he called" as "Je jouais au football quand il a appelé"It is constructed in the following way:Root + imperfect endingWhere the root is found by taking the 'nous' form of the verb, removing the 'ons' and adding the following endings:Je: -aisTu: -aisIl/Elle/On: -aitNous: -ionsVous: -iezIls/Elles: -aient