If you are a Dev Studio pro, you know that you need to do some work to configure a case type to have child case types under it.
In App Studio, we've automated the configuration so that you don't need to worry about it at all - it is all taken care of behind the scenes for you when you add the "Create case" automation to your case's process in case designer.
When you select this automation, you will select an existing case type or name a new case type that the automation will create a new instance of when it runs. If you name a new case type, a case type with that name will be created for you. The case type you have chosen (or created) will automatically be configured as a child case type for the case type that you are currently working on. That's all there is to it.
If you are curious, you can take a look at your case type in Dev Studio and you'll see that the configuration of the child case type has been done for you.