iOS : iCloud Container

The purpose of an iCloud container depends on what you want to do with it. (key-value, CloudKit...) You need it for an iCloud app.
The name of your iCloud container has to be the same in the Developer portal and in Xcode to let it work. Like I have an iCloud container for my app. In the Developer portal, in my app ID, iCloud is enabled and the container named "iCloud.com.xxx.xxx" (iCloud.com.name.app). In my app capabilities (in Xcode), iCloud is on and and container selected is the one with the same name.


References:
https://stackoverflow.com/questions/24191548/create-icloud-identifier-in-ios-developer-panel