Once you create your process flows you deploy your flows to Oracle Workflow or any compliant XPDL work flow engine.
You can also execute and schedule flows using Oracle Enterprise Manager. A quote from "OWB User Guide" states:
With Warehouse Builder, you have two main options for executing process flows: you can execute them from within Warehouse Builder using the Deployment Manager as described earlier, or you can execute them from Oracle Workflow. In addition, you can use Warehouse Builder to integrate with Oracle Enterprise Manager to schedule these process flow executions. For information about Oracle Workflow, see the Oracle Workflow Guide. For information about Oracle Enterprise Manager, see the Oracle Enterprise Manager Administrator's Guide.