Theory:

THE PAST - PAST SIMPLE AND PAST CONTINUOUS

The simplest way to look at THE PAST is to ask if it INCLUDES THE PRESENT or NOT.
For example:
I played tennis yesterday - this does not include THE PRESENT.
If I started playing 2 hours ago and I am still playing now, this action is IN THE PAST and is also IN THE PRESENT, so this is different.

There are TWO WAYS OF TALKING ABOUT THE PAST that does not involve the present.
The first case is if there was ONLY ONE ACTION.
For example:
I played tennis yesterday - this is called the PAST SIMPLE.

This uses DID in the negative and question forms.
For example:
I DIDN'T play yesterday. - NEGATIVE
DID you play yesterday? - INTERROGATIVE

The second case is if there were two actions that interrupted each other.
For example:
I played tennis and at the same time I saw you.
The correct form would be:
I was playing tennis when I saw you.
The ACTION THAT STARTED FIRST has the form was playing - PAST CONTINUOUS (to be + ing)

WHEN defines the moment of interruption.

The SECOND ACTION is in the form I saw you - this is the PAST SIMPLE.

This structure is ONLY USED IF THE ACTIONS HAPPEN AT THE SAME TIME.

If not, all the actions would be in the past simple.
For example:
Yesterday, I WENT to the cinema, I HAD a pizza, I MET Maria and I DRANK beer.