Past Progressive - Подлежащее + сказуемое (was/ were) + дополнение + обст. места + обст. времени.
I was reading a book at 5 o'clock yesterday.
They were playing computer games when their mother came home.
Past Simple - Подлежащее + Сказуемое (вторая форма глагола. если правильный - окончание -ed) и т.д.
I read a book yesterday.
They played computer games three hours ago.