Here is a summary of the three types of traversals that we covered with binary trees.

Preorder  - Middle, Left, Right
Inorder   - Left, Middle, Right
Postorder - Left, Right, Middle

The code for printing a tree in inorder would look something like...

public void printInorder(TreeNode root)  {
  if (root == null)
    return;
  printInorder(root.left);
  System.out.println(root.data);
  printInorder(root.right);
}

From what I said in section, you should be able to figure out the code for preorder and 
postorder traversals.

Here is an example.  Given the following tree,

     5
   /   \
  2     1
 / \     \
8  -1     9

Let's say I wanted to print the nodes.  Depending on the order, I would get different output...

Preorder  - output = 5,2,8,-1,1,9
Inorder   - output = 8,2,-1,5,1,9
Postorder - output = 8,-1,2,9,1,5

These are the three main types of traversals for binary trees.  If you want some practice, try
printing this tree in the three different orders above...

      +
    /   \
   6     -
       /   \ 
      *     9
     / \
    4   3

Read the answers in the next file specified in the section notes (NOTE: you may
want to read these notes even if you can do this with your hands tied behind your back... not
that you would need your hands or anything...)