Check the Roaming Status (EU and selected destinations) https://giffgaff.com/profile/details
If it is ON you can use your goodybag within the EU. If it is OFF, add some PAYG credit [link] and you will be charged 3.2p/min, 1p/SMS and 0.6p/MB (in addition to the cost of the goodybag). If staying in France more than a month, simply buy the £5 goodybag when your current one expires to keep getting the cheaper rates. If you do not have a goodybag you'll be charged the normal UK PAYG rates.