The Send Message Workflow Activity sends a Blue Integrator Message.  Each Send Message Activity is bound to a Send Port in the Blue Integrator Explorer when configuring a Workflow.  This activity is towards the top of the Activity Palette in the Blue Integrator Workflow Designer.

To use this activity in a Workflow, you must set the Message parameter, by selecting from the drop-down list of configured Blue Integrator Messages.  On execution, this is the name of the Message variable that will be sent to the corresponding Port.

Optionally you can configure the CorrelationFilter property, to determine which future messages will be directed to this Workflow Instance.  See the Correlation topic for further details.