To use your Custom Code Library from your Action Script code, you simply call the methods with ClassName.MethodName(..). For example DPccl.HelloWorld(). You do not need to specify the namespace where the class is defined.
The figure below shows an example where the variable q2 is assigned the value returned from DPccl.HelloWorld(). In this example, the custom code will be called for each data record in the source.
Figure 1 - Using the Custom Code Library from a Data Processing Action script