Choose a simple business process you are familiar with as a worker or customer. Use the Flowchart-BPMN template in Visio to create a Level0 diagram of the process. Include a sub-process in your diagram.
For help see:
http://office.microsoft.com/en-us/visio-help/bpmn-diagramming-basics-RZ102712773.aspx?CTT=1&client=1