Pay-per-day insurance uses your phone's location to detect when you're abroad, and charge you accordingly for those specific dates and regions.
For this to work correctly, you'll need to turn on location services on your mobile, so we can know when and where you go abroad. You will be notified when you are covered.
The price you will be charged for each location is made clear when you buy the policy from the 'Insurance' section of your app. If you travel a lot, don't worry, there's a cap on how much you will be charged in a year.