Let me post a photo of the example what we are talking about
This is a
single pole breaker
This is two pole breaker
There are few diffrent style but it will have two pole in there.
Now this is a
three pole breaker this typically used on three phase supply
Again this will have diffrent style and shape depending on breaker manufacter but basically it will give you a idea what we are talking about.
The single phase is used for one or two hots or line and in resdentail the one hot is 120 volts { north americiané side } while two pole will have 240 volts so that will make the diffrence.
The three pole is not very often used in resdentail side in North Americian side but if you have it let us know then we can cover the details on it later.
Merci,
Marc