The imperfect tense for all regular verbs in this tense is created by removing the ar/er/ir endings from the infinitive and adding the appropriate endings depending on the subject of the sentence (I, you, he/she etc). The appropriate endings are as follows:
AR verbsYo - abaTu - abas Usted - aba Nosotros - ábamosVosotros - abeis Ustedes - aban
ER/IR Verbs Yo - íaTu - íasUsted - íaNosotros - íamosVosotros - íaisUstedes - ían