action in the middle of happening at a stated past time
He was playing tennis at 4.30 yesterday.
past action in progress interrupted by another past action. The longer action is in the Past Continuous, the shorter action is in the Past Simple.
While I was get¬ting dressed the bell rang.
two or more simultaneous past actions
While I was sunbathing, Tim was swimming.
or background description to events in a story
She was flying to Paris.
The sun was shining...
past action which occurred before another action or before a stated past time
He had left by the time I got there, (or by 8.15)
complete past action which had visible results in the past
She was sad because she had failed the test.
the Past Perfect is the past equivalent of the Present Perfect
(He can't find his watch He has lost it) He couldn't find his watch. He had lost it.