The default service type is international priority
If the service type field is left empty in a FedEx connection, the international priority service is used. That is the right default for sellers shipping abroad quickly; but if you work domestically or with an economy service, every shipment is created at a more expensive service level than you expected. Setting the service type explicitly prevents the invoice surprise later.
You obtain your application keys through the project you create in the FedEx developer portal. The test environment has a separate address and separate credentials; test keys cannot connect to production.