Past background and interrupted actions in Brazilian Portuguese
Use a past situation or habit to set the scene, then say what happened against that background. Brazilian Portuguese often uses the pretérito imperfeito for the background and the pretérito perfeito for the main event. English translations can hide this distinction, especially when both verbs translate as simple past forms.
Enquanto: while; naquela época: back then
An action in progress and the event that happens during it
Enquanto situação em andamento no passado, acontecimento pontual no passado.
Enquanto eu lia, alguém abriu a porta.
Alguém abriu a porta enquanto eu estava lendo.
Use the imperfect for background conditions
In “Estava frio quando abrimos a porta.”, estava describes the background condition, while abrimos presents the door-opening as a completed event. English was does not distinguish background conditions from completed events in the same way Portuguese past forms can. Here, the cold is the setting for the event, rather than a new event in the story.
An ongoing action can also use the simple imperfect, as in lia, or estar in the imperfect plus a gerund, as in estava lendo. English speakers should not assume that was reading always requires the longer Portuguese form: both forms can describe reading in progress.
Estava frio quando abrimos a porta.
Describe repeated habits with the imperfect
Naquela época, eu atividade habitual no imperfeito expressão de frequência.
Naquela época, eu trabalhava todo sábado.
Eu geralmente trabalhava aos sábados naquela época.
Separate a usual habit from one particular occasion
In “Naquela época, nós geralmente comíamos em casa, mas uma noite fomos a um restaurante.”, comíamos describes the usual habit and fomos gives one particular outing. English can use the simple past for both ate and went, but Portuguese distinguishes their roles here. Naquela época establishes the past period, and geralmente makes the repetition explicit. The imperfect itself does not say that the habit still continues or explain why it ended.
Naquela época, nós geralmente comíamos em casa, mas uma noite fomos a um restaurante.
Back then, we usually ate at home, but one evening we went to a restaurant.
Tell overlapping actions apart from a sequence of events
In “Enquanto eu lia, alguém abriu a porta.”, the reading was already in progress when the door opened. This presents an event against a background; it does not necessarily mean that the person stopped reading. While translates as enquanto here, and the while-clause can come before or after the main clause.
In “Nós estávamos comendo enquanto as crianças dormiam.”, both activities form an ongoing background and overlap in time. In “Eu li o livro e depois fui dormir.”, li and fui instead present completed events in sequence. Choose the past forms according to how you present the situation, rather than treating enquanto as a word that automatically requires one tense.
Enquanto eu lia, alguém abriu a porta.
Nós estávamos comendo enquanto as crianças dormiam.
Eu li o livro e depois fui dormir.