When do we use Past Continuous?
For actions in progress at a past moment
Past Continuous describes an action that was in progress at a specific moment in the past. It is often used as a "background" action that was happening when something else occurred.
Something was happening at a particular moment in the past.
At 3 pm, Sam was riding his bike.
in progress at 3 pm
What were you doing at 8 pm last night?
specific past moment
She was sleeping when I called.
in progress when interrupted
A longer action (Past Continuous) was in progress when a shorter action (Past Simple) happened.
I was reading when he called.
was reading = background; called = interruption
She was cooking when the fire alarm went off.
background + interruption
They were playing football when it started to rain.
background + interruption
Two actions were both in progress at the same time — use "while".
While Sam was searching, Lena was asking neighbours.
both in progress simultaneously
While I was cooking, she was setting the table.
"while" for parallel actions
Past Continuous = the background/longer action. Past Simple = the interrupting/shorter action. "I was watching TV when he arrived." (was watching = background, arrived = interruption)