Past continuous (when vs. while)

[slavaj]

Hello. While I was reading a book I saw these sentences:
1) While we were waiting, it started to rain
2) I cut my finger when I was peeling the potatoes
3) While Dick was preparing lunch, he cut his finger
The question is when should I use while and when should I use when.

[Raymott]

Hello. While I was reading a book I saw these sentences:
1) While we were waiting, it started to rain
2) I cut my finger when I was peeling the potatoes
3) While Dick was preparing lunch, he cut his finger
The question is when should I use while and when should I use when.

"When" will generally mean "while" when there is a continuous action happening, as in all your examples (waiting, peeling, preparing). So you can use either for all those sentences.
When the action is a single action (in the simple past) you can't use "while" because there's no duration. "When he got out of the bath, he slipped over" (not "while")

[slavaj]

Thank you but I mean when should I use while and when should I use when in the past continuous. For example in the second sentence we have when (when I was peeling the potatoes) but in the third sentence we have while ( while dick was preparing lunch ) So, my question is what's the difference?

[Raymott]

Thank you but I mean when should I use while and when should I use when in the past continuous. For example in the second sentence we have when (when I was peeling the potatoes) but in the third sentence we have while ( while dick was preparing lunch ) So, my question is what's the difference?

As I said, you can use either.
If both clauses are continuous ("While I was sleeping, Mary was reading"), use "while".
If you're still not sure, you could give more examples, but I think that covers it.

[Rover_KE]

When in doubt, use when.

You will nearly always be right.

Rover