How do you form the imperfect tense?

With AR verbs, first take off the AR from your infinitive to get the stem of the verb, then add the imperfect endings as follows:Yo .....abaTú .....abasél/ella/usted .....abaNosotros ábamosVosotros abaisEllos/as/ustedes abanFor ER & IR verbs, remove the infinitve ending to reveal the stem, and then add:Yo .....íaTú .....íaél/ella/usted .....íaNosotros ....íamosVosotros ....íaisEllos/as/ustedes .....ían