The imperfect is another past tense that is used to express an action as going on in the past, as repeated or habitual. It is also used with mental and physical conditions and for descriptions. The preterite tense is used much more often than the imperfect tense though, except with these verbs: querer, creer, poder, esperar, tener, and saber. It is formed by adding these endings to the infinitive stem.
-er and -ir verbs
Yo vivía en España. I used to live in Spain.
Luisa estaba triste. Louise was sad.
El vendía radios. He was selling radios.
Only a few verbs are irregular in the imperfect tense:
ser – to be
ir – to go
ver – to see
Word Document at: 033 Spanish Imperfect Tense