The Workflow Node allows a Workflow to call another Workflow. This is comparable to a function calling another function in code and permits re-use of Workflows.
To add a Workflow to your current Workflow, click + on the Workflow Design Canvas. In the Choose Node or Workflow dialog that displays, click the Workflow tab and select a Workflow.
The chosen Sub-Workflow will be presented on the Design Canvas as a Node and the input and output properties defined in Variable Bar's on the Sub-Workflow will display as Properties on the Node.
If you change Properties in the Variable Bar's of the Sub-Workflow, you can refresh them in your Workflow by clicking the Node Header options button and choosing Refresh Properties.
You can also zoom into the Sub-Workflow by choosing Open Workflow from the Node Header options menu.