Process Editor is the canvas in which you design and create your process.
You can click on an activity in the activities palette located to the right of the Process Editor and drop it in the Process Editor by clicking anywhere within the process boundary or you can add an activity from the right-click menu accessible from within the Process Editor. Use Transitions to create a flow between the activities.
To open an existing process in the Process Editor, double-click the <process>.bwp in the Project Explorer. The process diagram will open in the Process Editor.