一个简单程序。

小弟没学过VC，哪位大哥能解释一下这个简单程序是什么意思，最好注释一下谢谢了越详细越好
#include "stdafx.h"MSG Msg;
char lpszClassName[]="WXNWINDOWS";
char lpszTitle[]="自定义窗口";LRESULT CALLBACK WinProc(HWND hwnd,
                        UINT message,
                        WPARAM wParam,
                        LPARAM lParam)
{
switch(message)
{
case WM_DESTROY:
PostQuitMessage(0); break;
        case WM_LBUTTONDOWN:
                        MessageBox(
NULL, // handle of owner window
 "点击鼠标左键", // address of text in message box
 "自定义窗口", // address of title of message box  
 MB_OK   // style of message box
              );
default:
return DefWindowProc(hwnd,message,wParam,lParam); }
return (0);}int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
  // TODO: Place code here.
                WNDCLASS wndclass;
                //窗口类的定义
                wndclass.style=0;
                wndclass.lpfnWndProc=WinProc;
                wndclass.cbClsExtra=0;
                wndclass.cbWndExtra=0;
                wndclass.hInstance=hInstance;
                wndclass.hIcon=LoadIcon(NULL,IDI_ASTERISK);
                //wndclass.hIcon=LoadIcon(xxx,"d:\\wxntest\\AUDIO.ICO"); //xxx为资源文件的句柄
                wndclass.hCursor=LoadCursor(NULL,IDC_ARROW);                //wndclass.hbrBackground=(HBRUSH)(COLOR_GRAYTEXT);
                wndclass.hbrBackground=CreateSolidBrush(RGB(255,0,0));
                //wndclass.hbrBackground=GetStockObject(WHITE_BRUSH);
                wndclass.lpszMenuName=NULL;
                wndclass.lpszClassName=lpszClassName;                if(!RegisterClass(&wndclass))
                {
                        MessageBox(
NULL, // handle of owner window
"失败！", // address of text in message box
"自定义窗口", // address of title of message box  
MB_OK   // style of message box
 );
                        return false;                }
//注册两次会失败！
/*
                if(!RegisterClass(&wndclass))
                {
                        MessageBox(
        NULL, // handle of owner window
        "失败！", // address of text in message box
 "自定义窗口", // address of title of message box  
MB_OK  // style of message box
        ); // return false;
                      
                }
               //创建一个窗口
                HWND hwnd=CreateWindow(lpszClassName,
                                       lpszTitle,
                                       WS_OVERLAPPEDWINDOW,
                                       CW_USEDEFAULT,
                                       CW_USEDEFAULT,
                                       CW_USEDEFAULT,
                                       CW_USEDEFAULT,
                                       NULL,
                                       NULL,
                                       hInstance,
                                       NULL);
                ShowWindow(hwnd,SW_SHOW );
                UpdateWindow(hwnd);

//可以创建两次以上！
                HWND hwnd1=CreateWindow(lpszClassName,
                                       lpszTitle,
                                       WS_OVERLAPPEDWINDOW,
                                       0,
                                       0,
                                       300,
                                       200,
                                       NULL,
                                       NULL,
                                       hInstance,
                                       NULL);
                ShowWindow(hwnd1,SW_SHOW );
                UpdateWindow(hwnd1);                while(GetMessage(&Msg,NULL,0,0))
{
  TranslateMessage(&Msg);
  DispatchMessage(&Msg);
}
return Msg.wParam; return 0;
}