It will allow one person to charge with a USB-C cable, and another person to charge with the other type of USB. Or for you to charge two such items at once.
You are mixing the "outlet" issue with the power/charging matter. The voltage different between Europe and North America is not an issue for modern electronic devices like phone and computers. (It IS an issue for some electrical items like hair dryers, so you must check the voltage range on the tag on those items.)
The plug on your device has two flat pins. The plugs in Europe have two round pins. You need something that will receive your flat-pins but which itself will plug into the round-pin receptacle ("outlet") in Europe. That is a minor physical adapting function. Very small adapters like this will work - you should use duct take to attach it so you won't leave it behind.
View attachment 176593
For
charging, you need something that will accept your phone cable (likely USB-A or USB-C) just like your charger does at home. However, you need to plug it into the European wall outlet, which is why you need either the small adaptor or a charger that was intended for use in Europe. In either, case, chargers are available that charge one or more devices at a time through USB cables.
The charging speed may vary with your device, the cable, and the charger. You can use the same charger you use at home, with the addition of the small adapter shown above. That charger may take one, two, or more devices at once.
If I have mis-stated anything, I hope someone will correct it!