The first statement creates the object (wfApp) that controls the running of a workflow. In that statement wf is the workflow. So you would then say wfApp.run() in order to run the wf workflow.
The second statement says that when the workflow completes then wfApp runs some code or method. In this case the code would be put into the brackets after the delegate.
This is covered in http://msdn.microsoft.com/en-us/library/dd560894(v=vs.110).aspx