Do anyone know why i got this error mesage ?

Linking...
msvcrtd.lib(crtexe.obj) : error LNK2001: unresolved external symbol _main
Debug/welcome.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

welcome.exe - 2 error(s), 0 warning(s)

Well, it has nothing at all to do with MFC. You probably created a console application and tried to code a MS-Windows win32 api application. You will probably have to start all over and create the correct type of application (win32 application).