To talk about an action in progress at a past moment, use was / were + the -ing verb. Use was with I, he, she, it; were with you, we, they.
was / were + -ing
At 8pm I was watching TV.
She was cooking dinner.
They were playing in the garden.
Not "They was playing in the garden." — say "They were playing in the garden.". With they, use were, not was.
Try it: At 8pm, we ___ dinner. (were having / was having / were have) Answer: were having — With we, use were, and add -ing to the verb: were having. "Was having" is for one person (I/he/she), and "were have" is missing the -ing.
Spelling the -ing verb
Most verbs just add -ing (play → playing, watch → watching). Verbs ending in -e drop the e first: drive → driving, have → having, make → making. Short verbs like run and sit double the last letter: run → running, sit → sitting.
She was driving to work. (drive → driving)
We were having lunch. (have → having)
The dog was running in the park. (run → running)
Not "She was driveing to work." — say "She was driving to work.". Drop the silent e before -ing: drive → driving, not driveing.
Try it: At noon, they were ___ lunch. (have) (having / haveing / haved) Answer: having — Drop the silent e before -ing: have → having. "Haveing" keeps the e by mistake, and "haved" is not a real form.
Negatives and questions
For the negative, put not after was/were: wasn't / weren't + -ing. For a question, put was / were before the subject: Was / Were + subject + -ing?
I wasn't sleeping at 10pm.
They weren't listening to me.
Were you waiting for the bus?
Was she working yesterday?
Not "Did you were working?" — say "Were you working?". For a question, move were in front of the subject — don't add did.
Try it: It was quiet. The children ___ any noise. (not / make) (weren't making / wasn't making / didn't making) Answer: weren't making — The children is plural, so use weren't and keep the -ing: weren't making. "Wasn't" is for one person, and "didn't making" mixes two past forms.
Try it: ___ you ___ TV when I called? (Were … watching / Did … watching / Was … watching) Answer: Were … watching — With you, start the question with Were and keep the -ing: Were you watching? "Did" doesn't go with -ing, and "Was" is for I/he/she/it.
A long action and a short one
When a short action breaks into a longer one, use was / were + -ing for the long action, and the plain past for the short one.
I was reading (long) when the phone rang (short).
She was driving when she saw the accident.
They were playing when it started to rain.
Try it: Amina was in the middle of cooking dinner. That took a while. Then, suddenly, the doorbell rang once. Which fits the longer action that was already happening? (She was cooking dinner. / She cooked dinner.) Answer: She was cooking dinner. — Cooking was the longer action already in progress, so use was cooking. "She cooked dinner" sounds finished, not the background to the doorbell.
Try it: Hiroshi was in the middle of a long drive. Then, in one quick moment, he saw an accident ahead. Which fits the short action that happened in one moment? (He saw an accident. / He was seeing an accident.) Answer: He saw an accident. — Seeing the accident happened in one quick moment, so use the plain past saw. "Was seeing" would make it a long action, but it was sudden.
while goes with the long action
While goes with the long action (was / were + -ing). When goes with the short action (the plain past).
While I was sleeping, the phone rang.
When the phone rang, I was sleeping.
While she was cooking, someone knocked.
Not "While the phone rang, I was sleeping." — say "While I was sleeping, the phone rang.". While goes with the long action (was sleeping), not the short one (rang).
Try it: Mei was reading for a long time. The phone call was the quick thing that broke in. Which word fits before the long action, was reading? (While she was reading, the phone rang. / When she was reading, the phone rang.) Answer: While she was reading, the phone rang. — Reading was the long action, and while goes with the long action: While she was reading, the phone rang. "When" usually points to the short action (when the phone rang).
Try it: While Lars ___ home, it ___ to rain. (was walking … started / walked … was starting / was walking … was starting) Answer: was walking … started — Walking home was the long action → was walking. The rain starting was the short moment → started. The long one takes was + -ing; the short one takes the plain past.