This stage of the BPM Cycle refers to run the business process diagram, and this can be done using the GXflow Desktop.
Because the BPD activities were associated to GeneXus objects, you can run a BPD object (pressing right mouse button over it and by selecting the Run option) and the Workflow engine will follow the execution flow of the diagram, invocating the corresponding application when it reaches each activity associated to a GeneXus object.
You should separate the concept of the Process Definition, which is related to de business process design information than the Process Instance, which is about the execution instance of a business process diagram. One Business Process Diagram object can be executed many times, and each one of those times is a different execution instance of the process.
The GXflow Client General Structure provides a user-friendly interface, with many functionalities to control de execution and monitoring of each of the instances process created by the Workflow Engine.