Now that you have seen the basic steps for interacting with QuickBooks via the Desktop SDK, and learned about the differences between developing with qbXML and QBFC, a great way to jump-start your first real project is to find a sample application that provides similar functionality and build on it.
For a list of sample applications in both qbXML and QBFC, sorted by programming language, with brief descriptions of the functionality each provides, see Sample apps and code.