Take file contents and put it into a string in C++

I'm using OpenGL and I need the contents of VertexShader.glsl to be put into a std::string

I've looked at the related StackOverflow posts about this but I don't really know how to match together data types and stuff to make it work.

Take for example this from Read file-contents into a string in C++

#include <fstream>
#include <string>

int main(int argc, char** argv)
{

  std::ifstream ifs("myfile.txt");
  std::string content( (std::istreambuf_iterator<char>(ifs) ),
                       (std::istreambuf_iterator<char>()    ) );

  return 0;
}

I have no clue what's happening after

std:: string content

Every time I have used std::string before has been like

std::string name = "2bdkid";