What is the use of NEW keyword in C++?

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C++98

I know the use of NEW keyword but i am confuse that what is main perpose of new keyword?
Some time we can do the same thing with other methods which we do with new keyword so need of clarification.
below is the example
I have created pointer object obj of class person and pass the address of object of student. I have write code in way so tell me the main difference?

What I have tried:

First code:

person *obj;
student s1;
obj=&s1;
obj.show();

2nd code:

person *obj;
obj=new student;
obj.show();