WF 4.0: How to Execute a Worklflow

 Here is something short and siple on how to execute a workflow using WorkflowInvoker vs WorkflowInstance. I really like this because it is quite simple and up to the point on explaining the concepts.
We can always dig deeper to get more insight.

http://blogs.msdn.com/bursteg/archive/2009/05/19/wf-4-0-how-to-execute-a-worklflow-workflowinvoker-vs-workflowinstance.aspx