Do you want a notification to show before the data is submitted asking them "Are you sure" or do you want to have the notification show up after it is submitted to say success?
Do you want to show a notification after the new item is submitted?
I agree with @Shanescows's thought almost, I think the Notify function could achieve your needs.
I have made a test on my side, please take a try with the following workaround:
Set the OnSuccess property of the Edit Form to following formula:
Notify("An item is created successfully!",NotificationType.Success)
More details about the Nofity funciton in PowerApps, please check the following blog: