Past tenses

The Past Simple is used to refer to:

Completed actions which happened at a specific time. I went to the cinema last week.
Completed actions and simulations which happened over a specific period of time. I lived and studied in Germany for three years.
Habitual actions or behaviour in the past. We played basketball in the street when I was a child.
A series of consecutive events in the past. He kissed her, said goodbye and closed the door.


The Past Continuous is used to refer to:

Temporary activities or situations in progress at a particular moment in the past. This time last week we were sitting on the beach.
A past activity or situation which was already in progress when another action ocurred (the activity or situation in progress may or may not continue). I was reading to my daughter when the lights went out.
Activities or situations occurring at the same time. Ann was cutting the grass while I was cooking.
The background events in a narrative. It was snowing heavily and a cold wind was blowing. 


The Past Perfect is used to:

Show that a past action or situation occurred before another past action or situation. When I saw Tom, he had just passed his driving test.
We used the continuous form to enphasize the duration of the first past action or situation. She had been waiting  for over two hours when he phoned to say he couldn't come.


Time linkers:

The past perfect is often used with time linkers. ex: after, before, by the time, as soon as, once, when, until. I couldn't go out until I had done my homework.

The past simple can be used if the order of events is clear. He sold his house before he left the country. Or if the second event occurred as a result of the first. When I realized what time it was, I ran outside.

After/afterwards. 
After is used to show the order of two or more events in the same sentence. Afterwards means "after that" and can go at the beginning or the end of a clause.

At last/in the end/at the end.
At last suggest that something good happends after a long period of time or more than one attempt.
In the end has a similar meaning and may also suggest there have been one or more changes or problems. They result may be good or bad.
At the end means at the point when something finishes.

When/as/while.
These can all be used with the past continuous to introduce an action which was already in progress when another action occurred.

During/in/for.
These are all used as prepositions when referring to time, and are followed by a noun. During and in are used to say when something happened. For is used to say how long something took or lasted.

Past Continuous or Past Simple?

Past Simple for a completed action in the past. She studied yesterday.

Past Continuous for an action in progress at specific moment in the past. They were studying when the TV program started.

Past Continuous: was/were + verb-ing

Past Continuous
	I/He/She/It		You/We/They
Positive	… was studying.		… were studying.
Negative	… wasn't studying.		… weren't studying.
Question/Ok/No	Was she studying?	Yes, she was.	Were they studying?	Yes, they were.
		No, she wasn't.		No, they weren't.

Use the past continuous to describe an action in progress at a specific moment in the past.