Reading head first design patterns and I'm currently reading about the observer pattern, is what I produced what the observer pattern is all about?

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

class ObserverInterface 
{
public:
    virtual void update(std::string message) = 0;
};

class concreteObserver : ObserverInterface 
{
    std::string name;
    std::string message;
public:
    concreteObserver(std::string name)
        :name(name)
    {}
    void update(std::string message)
    {
        this->message = message;

        std::cout << "Dear " << name << ", " << message << " from eBay" << std::endl;
    }
};

class SubjectInterface 
{
public:
    void subscribe(concreteObserver *subscriber)
    {
        subscribers.push_back(subscriber);
    }
    void unsubscribe(concreteObserver *subscriber)
    {
        subscribers.erase(std::remove(subscribers.begin(), subscribers.end(), subscriber), subscribers.end());
    }
    void notify(std::string message)
    {
        std::vector<concreteObserver*>::const_iterator itr = subscribers.begin();
        while (itr != subscribers.end())
        {
            (*itr)->update(message);
            ++itr;
        }
    }
private:
    std::vector<concreteObserver*> subscribers;
};

class concreteSubject : public SubjectInterface 
{
public:
    void newMessage(std::string msg)
    {
        notify(msg);
    }
};

int main(int argc, char* argv[])
{
    // EBAY
    concreteSubject ebay;

    // USERS
    concreteObserver user1("Steven");
    concreteObserver user2("John");

    // SUBSCRIBERS TO EBAY
    ebay.subscribe(&user1);
    ebay.subscribe(&user2);

    // EBAY SENDS NEW PROMOTIONS TO SUBSCRIBERS
    ebay.newMessage("enjoy free weekend listings");

    // UNSUBSCRIBE FROM EBAY
    ebay.unsubscribe(&user2);

    // EBAY SENDS NEW PROMOTION TO SUBSCRIBERS
    ebay.newMessage("free listings extended until 1st August");

    std::cout << std::endl << std::endl;
    system("pause");
    return 0;
}