Past Continuous Tense

What were you doing at 10 o'clock yesterday morning? Pick a card, show us and let us guess.

e.g. I was having breakfast.

I was swimming in the pool.

What was he doing at 7 o'clock yesterday evening?

He was sitting in the park.

What was she doing at 9 o'clock last night?

She was playing computer games. 

What were they doing at 11 o'clock last night?

They were eating a pizza.

In all these sentences we want to show the action in progress in the past. That is why we need the past continuous tense (past forms of TO BE + -ing). You should take care of the spelling (have --> having, swim --> swimming).