how to trace this code on paper..

[transgalactic]

i am getting lost with all he variables in each step

#include <stdio.h>
#include <stdlib.h>
typedef struct node {
  		int value;
  		int explored;
  		struct node *left;
  		struct node *right;
  		struct node *next;
} Node;

void add(Node **ptree, Node *n){  
  if (*ptree == NULL)
    *ptree = n;
  else
    if (n->value<(*ptree)->value)
      add(&(*ptree)->left, n);
    else
      add(&(*ptree)->right, n);
}

void push(Node **plist, Node *n){
  if (n){
      n->next = *plist;
      *plist = n;
  }
}

Node* pop(Node **plist){
  Node *n = NULL;
  if (*plist){
      n = *plist;
      *plist = (*plist)->next;
  }
  return n;
}

void what(Node *tree){
  Node *list = NULL;
  Node *n;
  if (tree){
      push(&list, tree);
      while (n = pop(&list)){
          if (!(n->explored)){
              n->explored = 1;
              push(&list, n->right);
              push(&list, n);
              push(&list, n->left);
          }
          else
            printf("%d ", n->value);
      }
  }
}
Node *create(int num){
  Node *n;
  n = (Node *)malloc(sizeof(Node));
  n->value = num;
  n->explored = 0;
  n->left = n->right = n->next = NULL;
  return n;
}

void main(){
   Node *tree = NULL;

   add(&tree, create(4));
   add(&tree, create(6));
   add(&tree, create(5));
   add(&tree, create(7));
   add(&tree, create(3));
   add(&tree, create(2));
   add(&tree, create(1));

   what(tree);
}