Marco,
I'm guessing that you are reading these messages from a news server, rather than from the NI website. Here is the text of the message referred to:
Howdy grassgnd,
So the overview that is discussed in the link above is that the OS sends a message to the WinProc (Windows Procedure) along with some parameters including the 2 message data parameters, WParam and LParam (data types of unsigned int and long). These parameter both specify additional information based on the message received. The message sent to the WinProc is of type integer and is usually expressed in constant form such as WM_CLOSE, WM_PAINT, etc.
In our case, we are using InstallWinMsgCallback which installs a callback function for a specific Windows message posted or sent to a LabWindows/CVI panel. The second parameter of InstallWinMsgCallback contains the message (integer).
Refer to the CVI shipping example msgdemo that demonstrates how to enable your panel to respond to any Windows message it receives. Locate this by selecting Help >> Example Finder >> Index tab (type the text "message").
Hope this clarifies a little bit for you.
Best Regards,