Explain following class, access modifire, inharitance, polimorphizom, function and veriables

#include<iostream>
using namespace std;
class Hospital_Database
{
protected:
    string Patient_Name;
    string Date_of_Admission;
    string Disease;
    string Date_of_Relaease;

public:
    void GetData()
    {
        cout<<"Enter Details of Patient:  "<<endl <<endl;
        cout<<"enter="" patient="" name:="" "<<endl;
        cin>>Patient_Name;
        cout<<"Enter Date of Admission:  "<<endl;
        cin>>Date_of_Admission;
        cout<<"Enter Disease of Patient:  "<<endl;
        cin>>Disease;
        cout<<"Enter Date of Release:  "<<endl;
        cin>>Date_of_Relaease;
    }

    void display()
    {
        cout<<"Patient Name:  "<<patient_name<< endl;
        cout<<"date of admission: "<< date_of_admission << endl;
        cout<<"disease patient: " << disease << endl;
        cout<<"release: " << date_of_relaease << endl;
    }
};

class getage : public hospital_database
{
private:
    int age;

    void get_age()
    {
        cout << "display information " << endl << endl;
        cout << "enter age patient " << endl;
        cin >> age;
    }

    void display_Age()
    {
        cout<<"Patient Age :  "<<endl;
    }
};

int main()
{
     getage p1;
     p1.getdata();
     p1.get_age();
     cout<<"display information of patient : "<<endl<<endl;

     p1.display_age();
     p1.display();

     return 0;
}