From ReliCodia

int WinMain (HINSTANCE hInstance,
             HINSTANCE hPrevInstance,
             LPSTR lpCmdLine,
             int nCmdShow)

Every GUI Windows program must define this function. It is used instead of the main of non-GUI programs. It is the entry point of the program.

hInstance Instance handle of the current executable module.
hPrevInstance NULL. No longer used by Windows.
lpCommandLine The command line with which the program was called, without the exe name. Access to the full command line is possible through GetCommandLine
nCmdShow CmdShow parameter specifying how the main window will be shown.