I need to understand how a C++ listnode can have link a list class with three member functions and a default constructor such as void add (double x);...

I need to understand how a C++ listnode can have link a list class with three member functions and a default constructor such as void add (double x); boolean ismember (double x); int search(double x); LinkedList(); which can return position of a number x on list while first node at 0; second at 1; and etc, with no x returning -1.