basic question on boost.python

I just started to learn boost.python .  But I'm getting confused by the simplest
"hello world" example on the boost website:

Here's the C++ program:
char const* greet()
{
   return "hello, world";
}

and the wrapper:

#include <boost/python.hpp>
using namespace boost::python;

BOOST_PYTHON_MODULE(hello)
{
    def("greet", greet);
}

My first question is, which one is inside the "hello.cpp"?  Or both?
My second question is, shall I how to create a library that python can load? 
Shall I just type   "gcc -fPIC hello.cpp" ?  Thanks a lot!


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