Not getting the code

#1

what are istream and ostream and what is the use of these fucntion.

and also dont understand what are the meaning and importance of these fucntions.

ostream& operator<<(ostream &os,nodehead);
istream & operator>>(istream &is,nodehead);

#2

For this you must first refer and learn operator overloading concepts. It must be taught in the OOPS section of your course. Check that section.