I think, more specifically you're looking for:
http://msdn.microsoft.com/en-us/library/dd339004.aspx
Creating a codeunit from within Microsoft Dynamics NAV.
Exposing the Web service.
Verifying the Web services availability.
Consuming the Web service from a console application that is created in Visual Studio
Just make sure you have
- Microsoft Dynamics NAV 2009 with a developer license.