how will we create a date header file in which user must be able to perform:
1: get and set current day,month and year.
2: increment by x number of days,months and year.
3: set default date.

default date should be declared as a static member.

I think you mean you want to know how to create a date class. Do you know how to create a class of any type? The three items you listed could be methods of the class. The data objects of a date class would contain day, month and year integers, as you might expect.