Problem on programming by using VS2012

Hi programmers,
in these, after several years on using Visual Studio 6, I migrate to Visual Studio 2012 and I start with troubles.
I suppose that I lost several informations in these years, but I neither able to use CString or Messagebox() and, obviously, some frustration got over me.
Could you please tell me what was wrong?
I reported just a couple of line of easy code, just to understand what is wrong.

CString str;
int a =4;

str.Format("%d",a); // <==== FAIL
MessageBox("Help, Something went wrong."); <==== FAIL

MessageBox(_T("Help, Something went wrong."));
MessageBox(stra);


Before I could write just MessageBox("test"); without problem, now it seems not possible, I must declare _T

MessageBox(_T.......

Moreover It seems that str.Format("%d",a); could not be used anymore, why?

Sorry for the low level of my question, but if you could clarify these easy problem, I would be gratefull.
Have a good day.
Ciao
Sergio