The Past Simple Tense shows that an action took place in the past:
I met him yesterday. My grandmother once saw Queen Victoria. The train was ten minutes late.
The Past Continuous Tense denotes an action/a process which was going on at a certain moment or quite a short period of time in the past. And this time must be always indicated:
I had played football yesterday.
I was playing football at 17 o'clock yesterday.
My children were watching TV from 18 till 21 o'clock yesterday.