The Past Continuous is used to denote an action in progress going on at a definite moment in the past. This definite moment can be expressed in two ways, - either by an adverbial phrase with the preposition at or by another action in the Past Indefinite.
At seven o'clock he was still waiting for her at the entrance to the metro-station.
В семь часов он все еще ждал ее у входа в метро.
When Boris came, Pitter and me were playing chess.
Когда Борис вошел, мы с Питером играли в шахматы.
The Past Continuous can be used emphatically instead of the Past Indefinite to denote a customary repeated action in the past when the speaker wants to represent it as a continual process showing his emotional attitude to this action (usually negative).
She was always complaining of somebody.
Она постоянно жаловалась на кого-то.
The Past Continuous is often used in adverbial clauses of time introduced by the conjunction while.
There are two models here:
In the first model the actions are represented as parallel processes.
In the second model one action took place against the other.
While she was making coffee, I was watching TV.
Пока она делала кофе, я смотрел телевизор.
While she was making coffee, I called the box-office and booked tickets to the cinema.
Пока она делала кофе, я позвонил и заказал билеты в кино.
The Past Continuous can be used emphatically instead of Past Indefinite to denote a simple action in the past when the speaker wants to emphasize the duration of an action. It often takes place with such emotional phrases as from morning till night, all day long, for a whole hour.
I was preparing for my test all day long.
Я весь день готовился к контрольной.
I was sitting in the Public Library from morning till night yesterday.
Вчера я с утра до вечера просидел в публичной библиотеке.
The Past Continuous can be used to denote an action whose duration is limited by a certain event.
When I was on a business trip in Munich, I was staying at the Four Seasons hotel.
Когда я был в командировке в Мюнхене, я останавливался в отеле Four Seasons.
What were you wearing at the concert yesterday?
Что ты одевал на вчерашний концерт?