_tmain() is a Microsoft extension, it doesn't exist in C++ or any compiler not MS. Better off to not use it unless you are writing code needing to be compiled as ANSI or UNICODE.
You'd be better off never using MS extensions to the C++ language. C++ with a bit of due diligence works just fine for ANSI or UNICODE.
I see you are using Visual Studio 2008. That is very much outdated.
Unless you are required to use VS2008 I would recommend getting Visual Studio 2017. It is free to use. 2008 won't let you compile C++11 or later specific code. That can be a serious block to learning C++.