We use the past continuous to talk about the situations that were happening in the past. The past continuous is formed from the past tense of the verb be, together with the -ing form of a verb.
Last Friday Sue went swimming. She started to swim at 9.00 a.m. and finished at 10.30 a.m.
What was Sue doing at 9.30 a.m.? Sue was swimming at 9.30 a.m. She had not finished swimming at 9.30 a.m. She was in the middle of swimming at 9.30 a.m.
She was always singing in the bath.
They were helping each other all the time.
All the employees were demanding.
His arm was aching.
Our little town was rapidly growing.
Also, we often use the past simple and the past continuous together to say that something happened in the past.