If process resources are only to be used within a Business Process, they can be created directly within a parent process. This means that they can only be used in the process context and cannot be called up from other Business Processes.
In general, the same resources can be created within a single Business Process as within a BPM project - be it further Business Processes (.bpm), Technical Processes (.wrf), human tasks (.humantask), rules (.rule) or domain models (.domainmodel).
The resources to be used can be created both via the context menu New > <resource name> and via the toolbar 
The created resources can then be parameterised as usual and incorporated into the process diagram via drag & drop from the repository, see also Human Task, Rule, Managing Domain Models.