[c-prog] (beginner) .h and .cpp

[Jos Timanta Tarigan]

Hi folks,
Im new to C++ and currently developing C++ under os x. 

Im a little bit confused the difference between .h and .cpp. What is actually a 
.h file? What is the difference between .h and .cpp? I actually implement all 
my methods at .h file so my .h file look like this:

#include <iostream>

using namespace std;

class Person
{
        public:
        Person::Person(string input)
        {
                userName = input;
        }

        void Person::setFirstName(string input)
        {
                firstName = input;
        }
        private:
                string userName;
};


Is there any convention/trade off with this method?

Thank you 


Regards

Jos Timanta Tarigan