The past continuous tense is used to describe:
1. an unfinished action in the past that was interrupted by another action;
Imagine you started to watch a TV program at around 7 pm last night. You continued to watch it for a few minutes. When you were in the middle of watching the program, which means your watching TV was still in progress, the phone rang. The action of watching TV was interrupted by the ringing telephone.
In this case, we should use the past continuous tense to describe the interrupted action (of watching TV), and the simple past tense to describe the action that interrupted. Thus, the sentence to describe the two actions will look like this:
I was watching a TV program when the telephone rang.
Notice the use of when to combine the two actions. It is possible to put the sentence this way:
When I was watching a TV program, the telephone rang.
Note that we can also use while in the place of when in the above sentence.
Whle I was watching a TV program, the telephone rang. (correct)
However, we cannot say:
I was watching a TV program while the telephone rang. (incorrect)
Picture another action. Imagine you started to read a novel at around 7.30 pm last night. You continued to read it for a few minutes. When you were in the middle of reading, which means the action of reading was still in progress, the light went out. To describe the interrupted action, you should use the the past continuous tense, and to describe the action that interrupted, you should use the simple past tense. Thus, the sentence to describe the two actions will look like this:
I was reading a novel when the light went out. OR
When I was reading a novel, the light went out. OR
While I was reading a novel, the light went out.
I was reading a novel, while the light went out.
2. the background in a story.
Read the following:
The sun was shining brightly, the birds were singing, perking on the branches of trees, and the breeze was blowing gently when I opened the windows. I woke up earlier this morning because I had to get to school 15 minutes earlier than usual.
3. an action in progress at a specific time in the past
For this use, a specific time in the past, e.g. 7 o’clock pm, this time yesterday, etc.
a. I was eating dinner at 7 o’clock last night.
(This means I started eating earlier, and at 7 o’clock I was in the process of eating dinner)
b. They were playing pocker this time yesterday.
(This means they started playing pocker earlier, and they were in the process of playing)
c. My dad was fixing the bicycle at 4 o’clock pm.
(This means my dad started fixing the bicycle earlier, and he was in the process of fixing it)
4. two actions that were happening at the same time (parallel actions)
a. I was studying history while Maria was studying math.
b. Andi was watching TV while Toni was playing a video game.
Remember that the past continuous of a verb is made up of two parts: was/were and the base form of a verb + ing.
Ana was watching TV when the lightning struck. (affirmative)
Ana was not watching TV when the lightning struck. (negative)
Was Ana watching TV when the lightning struck. (interrogative)