Past continuous: I was doing …

Past Continuous is about an action, an activity in the past.
Past Simple is about a past event as a simple fact !
Past Continuous is about the past events, BUT with a continuing process of an activity.
I was just making some coffee.
I was thinking about you last night.
While I was driving home, my wife was trying to contact me.

Past Continuous is used to describe an action in the past when something else happened.
I was playing the piano when I heard the phone.
We were walking in the street when he suddenly fell over.
We were talking about you before you arrived.

CONSTRUCTION:
to be past form (was/were) + infinitive + -ing

AFFIRMATIVE and NEGATIVE FORMS: 

Situation in the past:
Yesterday, i worked. I arrived at the office at 9.00 am, and finished at 6.00 pm.
So, yesterday, at 11.00 am, I was working.
9.00 ———> 11.00———> 18.00 ———-> Today
Past —–—-> Past———–> Past ———-> Now

I was doing sth at 11.00
I started / I finished doing sth
Past Continuous: I was doing something:
That means at a certain period, I was in the middle of an action.
The situation started before this time, in the past, and had not finished.
USE: we use the Past Continuous when the action is not finished.
I was doing something when Peter called me.

Past simple: (-ed) : Action is in the past , but finished!
Past continuous: (was/were + Infinitive + ing) : Action is in the past, but not finished.
I was walking when somebody asked me the time.
I was taking a bath when the phone rang. (ring, rang, rung)
I was watching the soccer on TV when my wife arrived.
We were eating when our grand parents rang us.

But:
I walked home after the party last night. (the activity is finished!)
I watched TV everyday when I was at the hospital. (the activity is finished!)
Non-continuous Verbs:
Non-continuous Verbs are not used with the Past Continuous.
These verbs are « stative », about state, and not real action or activity.
So, they can’t express a continuous or progressive form.

Here, we present you the most common non-continuous verbs:

Notice: with SEE & HEAR, we often use CAN:
I can see you.
I can’t hear you.

We don’t use the continuous form with these verbs, because ther’s not a real action.
Look differences:

PAST:

• 006c: Past Simple: « to be »: I was
• 006d: Past Simple: « to do »: I did 
• 007:   Past Continuous: I was doing …  
• 007:   Past Continuous: I was doing, when we dont use this form
• 008:   Past Simple (I did) and Past Continuous (I was doing)