The main difference between a function and a method is that a function can live independently of the any instance of a class, where as a method sits within a class.
That is about it, e.g. a function is
int func(int value);
...
int main()
{
cout << funct(3) << endl;
}
whereas a method has to live within a class
class myclass
{
int myMethod(int it);
};
....
int main()
{
myclass theclass;
cout << theclass.myMethod(4) << endl;
}