(1)
The imperfect tense is formed by taking the nous form of the present tense. For the verb 'jouer' (to play), for example, the nous form is 'jouons' (as in nous jouons).
The -ons is removed from the verb, leaving 'jou' and the imperfect endings (ais, ais, ait, ions, iez, aient) are added:
je jouais
tu jouais
il/ elle/ il jouait
nous jouions
vous jouiez
ils/ elles jouaient
(2)
2 exceptions to this rule are commencer and manger.
Verbs like manger add an extra -e before -a, -o, -u.
Nous mangeons becomes:
je mangeais
tu mangeais
il/elle/on mangeait
nous mangions vous mangiez
ils/elles mangeaient
With verbs like commencer, the last -c becomes -ç before -a, -o, -u. Nous commençons:
je commençais
tu commençais
il/elle/on commençait
nous commencions
vous commenciez
ils/elles commençaient
NB. The endings for the imperfect tense are always the same.