Simple Past vs. Past Progressive Tense

Remember- the simple past talks about something that happened before. It happened and it finished. Some words are regular and just have -ed added at the end like walked, helped, and played. Others are irregular and have many variations like ate, began, and slept.
The past progressive talks about something that was happening before, but for a period of time. It uses was or were + verb-ing like was eating or were playing. It gives a background for something that was happening while a different event happened.

Example: While I was eating, the telephone rang.

So, during the time I was eating (let's say from 6:30-7:00 p.m.) somebody called my house (let's say they called at 6:49 p.m.) One thing happened (simple past) during the period of time another thing was happening (past progressive.)

Here is another example: They saw an old man as they were walking down the street.

You can think of walking as a video. You see the movement. You see the time passing. Think of saw as a photo. It is one point of time. You don't think of the time passing.

I dreamed in English when I was sleeping.
She was listening to the radio when the mail came.
They visited Sydney when they were traveling in Australia.