First you have to open the detail view in the cockpit for the correct SIM card.
It works like this: Where can I view/change the SIM details?
Then activate the individual fields of your choice in the detailed information of your SIM card.
Charges are only incurred for services actually used.
You can find more information about the costs here: How much do voice roaming and value-added services cost?
You can find more information about the different zones (countries) and the standard rates under the following link: To the tariff overview