IMPERFECT PAST TENSE - VERBS ENDING IN -AR, -ER, IR ( PART 1 ) :

The Imperfect Past Tense is used:

a. To express habitual action in the past as expressed in English by "used to":

Ele viajava muito .............. He used to travel a lot.
Eu dançava bem ............ I used to dance well.
Estudávamos pela manhã ......... We used to study in the morning

Notice the difference between the perfect past and the imperfect past tenses in the examples below :

Ontem eu visitei Petrópolis ( Yesterday I visited Petrópolis) - a completed action in the past.

Quando menino, eu viajava muito com meu pai. ( When I was a boy I used to travel with my father) - a habitual action in the past,.

Ref.: Learning Portuguese . Ed. Disal.