توضیح درباره زمان‌های گذشته‌ی کامل و استمراری

The simple past expresses completed past actions .
For example :
I washed my hair last night

The past continuous expresses a past activity that has duration .
For example :
I was washing my hair when you called .

We use the past perfect to express a past action that happened before another action in the past .
For example :
When l arrived at the theater , the play had already started .

لینک زیر هم می تونه کمکتون کنه.