We use past continuos when we talk about an action that start in the past and hasn't finish or you don't know that the action is finish.
I was working in the factory
I was going to the cinema
We also use past coninuos when we talk about an action that iterupt's another.
I was having a bath when the phone rang
I was eating a cake when i saw a gost
past continuos is made by
was/were + infinitive + -ing