The imperfect tense is one of the two tenses used to describe the past tense form in Spanish. It is one of the most regular tenses used in Spanish. The imperfect tense is formed by adding the imperfect ending to the stem of the word. Words that end in –ar have "–aba" endings and verbs ending in -er or –ir have "–ia" endings.

yo cantaba
I sang
tú cantabas
you sang
él/ella/usted cantaba
he/she/you sang
nosotros cantábamos
we sang
vosotros cantabais
you sang
ellos/ellas/ustedes cantaban
they/you sang
yo movía
I moved
tú movías
you moved
él/ella/usted movía
he/she/you moved
nosotros movíamos
we moved
vosotros movíais
you moved
ellos/ellas/ustedes movían
they/you moved
yo dormía
I slept
tú dormías
you slept
él/ella/usted dormía
he/she/you slept
nosotros dormíamos
we slept
vosotros dormíais
you slept
ellos/ellas/ustedes dormían
they/you slept

There are three verbs that are irregular in the imperfect tense. They do not follow a pattern, so they must be remembered.
The verbs are ser,ir and ver.

yo era
I was
tú eras
you were
él/ella/usted era
he/she/you was
nosotros éramos
we were
vosotros erais
you were
ellos/ellas eran
they/you were
yo iba
I went
tú ibas
you went
él/ella/usted iba
he/she/you went
nosotros íbamos
we went
vosotros ibais
you went
ellos/ellas/ustedes iban
they/you went
yo veía
I saw
tú veías
you saw
él/ella/usted veía
he/she/you saw
nosotros veíamos
we saw
vosotros veíais
you saw
ellos/ellas/ustedes veían
they saw

1. The imperfect tense can be used to describe background actions of the past.
- Eran las ocho y media cuando llegamos a la casa. (It was eighty thirty when we arrived at home.)
- Cuando fuimos a nadar hacia calor. (When we went to swim it was hot.)
2. It can be used to describe to describe routine actions that occurred in the past.
- Cuando mi madre vivía en Guatemala, comía muchas tortillas. (When my mother lived in Guatemala she ate a lot of tortillas.)
- Siempre nos reíamos en la clase porque nos divertíamos juntos. (We always used to laugh in class because we would have fun together.)
3. It can describe circumstances of the past.
- Cuando yo era un niño no teníamos una television porque vivíamos mas simples. (When I was a child we didn’t have a television because we led a simple life.)
- En Argentina se comía mucha carne. (In Argentina a lot of beef was eaten. )
4. The imperfect tense also describes progressive past actions or actions that occurred repeatedly in the past without a reference to when they began or when they ended.
- Cuando vivía en casa lavaba trastes cada dia. (When I lived at home I washed dishes every day.)
- Mi sobrino iba al parque cada fin de semana cuando era chiquito. (My nephew went to the park every weekend when he was little.)