Past continuous

((+)) Subject + WAS/WERE + [verb+ing] + objects 

was (I, he/she/it) --> She was playing football yesterday when you arrived home. 

were (you, we, you, they) --> You were eating an apple. 

((-)) Subject + was/were + NOT + [verb+ing] + objects --> She wasn't playing football yesterday. 

(wasn't / weren't)   --> You weren't eating an apple. 

((?)) Was/Were + subject + verb (infinitive! not past!!) ?  --> Was she playing football yesterday? 

--> Were you eating an apple?

We use the past continuous to describe past actions or states which were incomplete or in progress at a specific time in the past.

Yesterday morning we were sitting outside.

At nine o’clock last night, I was writing my essay.

We can use the past simple with the past continuous and when or while to describe an activity that was happening when another activity interrupted it.

I was walking home when I saw Paul.

While I was driving, my phone rang. // My phone rang while I was driving.

We never use the continuous form with stative verbs. Stative verbs express a state – not an action. Since there is no action in progress, the past continuous should not be used. 

I didn't know the answer. I was not knowing the answer.

She really liked you. She was really liking you.
He seemed happy at that moment. He was seeming happy at the moment.

The most common are verbs that express:

• thoughts and opinions: believe, know, understand, remember, forget, think ...

• preferences: like, love, prefer, hate ...

• a state or possession: be, have (got), own

Verbs that are sometimes stative

A number of verbs can refer to states or actions, depending on the context.

I think it's a good idea.
Wait a moment! I'm thinking.

The first sentence expresses an opinion. It is a mental state, so we use present simple. In the second example the speaker is actively processing thoughts about something. It is an action in progress, so we use present continuous.

Some other examples are:

have

I have an old car. (state – possession)
I'm having a quick break. (action – having a break is an activity)

see

Do you see any problems with that? (state – opinion)
We're seeing Tadanari tomorrow afternoon. (action – we're meeting him)