We use the past simple to talk about actions and states which we see as completed in the past.
We can use it to talk about a specific point in time.
* She came back last Friday.
* I saw her in the street.
* They didn't agree to the deal.
It can also be used to talk about a period of time.
* She lived in Tokyo for seven years.
* They were in London from Monday to Thursday of last week.
* When I was living in New York, I went to all the art exhibitions I could.
You will often find the past simple used with time expressions such as these:
* three weeks ago
* last year
* in 2002
* from March to June
* for a long time
* for 6 weeks
* in the 1980s
* in the last century
* in the past