What mean of various headers

Answer 1

The headers are libraries of predefined C++ functions, classes objects and other things.

http://www.cplusplus.com/doc/tutorial/program_structure/

Answer 2

you can add as much header file as per the program needed

Answer 3

You don't need to know that at your current level because you have to know OOP(object oriented programming)
for knowing this.

briefly its a way that you can include your one code's data to another code