Past continuous!

It's formed by: the verb to be in past + the verb ending in -ing.

I was jumping
You were jumping
He/she was jumping
It was jumping
We were jumping
You were jumping
They were jumping

Negative:
I not/wasn't jumping
You weren't jumping
He/she wasn't jumping
It wasn't jumping
We/you/they weren't jumping.

Interrogative:
Was I playing
Were you playing?
Was He/she/ it jumping?
Were we/you/they jumping?

Answer:
Yes, I was jumping
No, you wasn't jumping
Yes, he/she/it was jumping
No, we/you/they weren't jumping.

We use it to express an action that it was in progress or if we don't know it's ending.

To express two actions that are in progress in the same moment.
Ex: I was wathing the tv, while the telephone rang.

To express two actions that are in progress in the past, that one of them starts before than the other.
Ex: when I arrived, John was talking on the phone.


Credits: http://www.intercambio-es.com/es/curso.php?id=34, and some of the grammar book.
(the two entries)