Dates *myEaster;
is a pointer of type Dates called myEaster
a pointer of type Dates points to a Dates object. In the wild that pointer may only point to a Dates object or nothing (i.e. nullptr).
Dates *myPtr
is a poorly named pointer of type Dates called myPtr
void GetEaster(Dates *myPtr);
myPtr will point to whatever argument gets passed to the function, like for example:
myDates.GetEaster(&myDates);
is a pointer to the myDates object.
the address-of operator is how you turn the object into a pointer to the object, as demonstrated in that code.
I have to say, the variable names (if they are used that way in the book) are rather suckish.