To write hello world program in c++ first we need to understand what is header files. In C++ we use <iostream> header file. iostream stands for input output stream. in modern c++ we don't use .h as a header file extension.
cout is used to print on screen in c++ and cin is used to take input from the user in c++.
Namespace is the collection of classes. The using staement inform the compiler that you want to use the std namespace. Entire standard c++ declared in this namespace.
#include<iostream>
using namespace std;
int main(){
cout<<"Hello World!! How are you? How's the weather today?";
return 0;
}