MFC Visual C++ (Beginner)

[Shawn N]

I have this bit of coding out of Ivor Horton's "Introduction to Microsoft Visual C++ 6.0". Book is great and everything but this is the extent of an actual Windows app. Anyone mind throwing out a little coding for a button that would do something simple like a MessageBox or changing the main window's title?

#include <afxwin.h>        // For the class library

// Window Class definition
class COurWnd : public CFrameWnd
{
};

// Application class definition
class COurApp : public CWinApp
{
public:
    virtual BOOL InitInstance();

private:
    COurWnd* GetMainWindow() { return static_cast<COurWnd*>(m_pMainWnd); }
};

// Function to create an instance of the main window
BOOL COurApp::InitInstance(void)
{
    // Construct an object of our C++ window class
    m_pMainWnd = new COurWnd;

    // Call Create() to create the underlying window
    GetMainWindow()->Create(NULL, _T("Our Simple Window"));

    // Call ShowWindow() to display the window
    GetMainWindow()->ShowWindow(m_nCmdShow);
    return TRUE;
}

// Application object definition oat global scope
COurApp AnApplication; 

If anyone wouldn't mind giving an explanation of what's going on with things like "virtual BOOL InitInstance();" (what the hell is virtual?!) or the line "class COurApp : public CWinApp (what's with the public CWinApp after the colon?) it'd really be appreciated.