What is std:: used for in C++?

I read the question about What's the purpose of: "using namespace"?. It is similar to this question but didn't really answer it. I am new to C++ and was wondering what the std pointer really does? Here's an example:

#include <iostream>

int main()
{
     std::cout << "Hi, Earth!\n" << endl;
}

So, what does the std:: do?