Window API始めたての頃、ウィンドウ作成する時によくわからなかった事

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine, int nCmndShow)
{
	const wchar_t className[] = L"main_window";
	const wchar_t title[]     = L"test";
	MSG msg;
	BOOL bRet;

	WNDCLASSEXW wcex;

	wcex.cbSize        = sizeof(WNDCLASSEX);
	wcex.style = CS_HREDRAW | CS_VREDRAW; // | CS_DROPSHADOW;
	wcex.lpfnWndProc   = MainProc;
	wcex.cbClsExtra    = 0;
	wcex.cbWndExtra    = 0;
	wcex.hInstance     = GetModuleHandle(nullptr);
	wcex.hIcon         = LoadIcon(wcex.hInstance, nullptr);
	wcex.hCursor       = LoadCursor(nullptr, IDC_ARROW);
	wcex.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
	wcex.lpszMenuName  = nullptr;
	wcex.lpszClassName = className;
	wcex.hIconSm       = LoadIcon(wcex.hInstance, nullptr);

	if (!RegisterClassExW(&wcex))
		return FALSE;

	HWND hWnd = CreateWindowExW
	(
		w_style_ex.at(i),
		className,
		ex_style_n[i],
		w_style.at(k),
		500,
		300,
		300,    //幅 
		200,    //高さ
		nullptr,
		nullptr,
		GetModuleHandle(nullptr),
		nullptr
	);

	if (!hWnd)
		return FALSE;

	//if (!SetLayeredWindowAttributes                        //レイヤー時に使用
	//(/*_In_ HWND hwnd      */ hWnd
	//	,/*_In_ COLORREF crKey */ RGB(0xff, 0xff, 0xff)
	//	,/*_In_ BYTE bAlpha    */ 150
	//	,/*_In_ DWORD dwFlags  */ LWA_ALPHA
	//))
	//	return false;

	ShowWindow(hWnd, nCmndShow);
	UpdateWindow(hWnd);

	while ((bRet = GetMessage(&msg, nullptr, 0, 0)) != 0)
	{
		if (bRet == -1)
			break;

		else
		{
			TranslateMessage(&msg);
			DispatchMessage(&msg);
		}
	}
	return 0;//(int)msg.wParam;
}