How do I use the imperfect in French?

In French, the imperfect is used

- to describe a scene  eg. il PLEUVAIT dehors

- to say that you did something on a regular basis in the past eg. je COURAIS chaque lundi matin

- or to describe a continuous action in the past eg. il ROULAIT  très vite sur l'autoroute.

It is formed by taking the infinitive from 'mang-er', 'roul-er', 'dorm-ir' and adding the endings (-ais, -ais, -ait, -ions, -iez, -aient).  However, you must be careful with irregular verbs, which are the same as those in the present tense. For those you take the 'nous' form of the present, taking off the 'ons' and adding the endings (ais, ais, ait, ions, aient). For example, if I want to say "you (plural) used to say", I would take the nous form of the present (nous disons), take off the ending and add iez. "Vous disiez".