Windows Workflow Foundation (WF) provides a programming model, in-process workflow engine and rehostable designer to implement long-running processes as workflows within .NET applications. Workflows are built using activities, which define units of work. These activities are composed together into a tree of activities that are then executed by the runtime. Workflows can be created using the workflow designer hosted inside of Visual Studio, created using code or XAML, and the workflow designer can be rehosted in a custom .NET application outside of Visual Studio.
There are many good resources for getting started with WF. The .NET Framework Developer Center for WF (on MSDN) has many good resources. There are also some introductory screencasts here, and two good whitepapers in the MSDN Library: The Workflow Way: Understanding Windows Workflow Foundation and A Developer's Introduction to Windows Workflow Foundation (WF) in .NET 4. The WF MSDN documentation contains a Getting Started Tutorial which walks through the basic steps of creating workflows and hosting them. There are also hands-on labs for WF. They are available as part of the Visual Studio 2010 and .NET 4 Training Kit on the Microsoft Download Center, (which includes labs for many areas of .NET 4 and VS other than WF), and are also available integrated within Visual Studio from the Ron Jacobs MSDN blog.
Read the rest here, including lists of resources.