It think it's clearer with code:

/* API header */

struct pt
{
  int x;
  int y;
};

extern struct pt *ptcreate(int x, int y);
extern struct pt *ptdestroy(struct pt *ptr);

/* API source file */

struct pt *ptcreate(x, y)
  int x;
  int y;
{
  struct pt *ptr = (struct pt *) malloc(sizeof (struct pt));

  if (ptr == (struct pt *) NULL)
  {
    return (struct pt *) NULL;
  }

  pt->x = x;
  pt->y = y

  return ptr;
}

void ptdestroy(struct pt *ptr)
{
  if (ptr == (struct pt *) NULL)
  {
    return;
  }

  free(ptr);
}

/* program source file */

#include <api.h>

int main()
{
  /*
    the scope of ptr start here and it takes the return value of
    the ptcreate function
  */
  struct pt *ptr = create(0, 0);

  ptdestroy(ptr);
}