How to fix error BCE0005: Unknown identifier

I'm making a zombie apocalypse game. I copied some code from http://www.instructables.com/id/Intro-to-Unity/step13/HUD-and-Menu-system/ and http://www.instructables.com/id/Intro-to-Unity/step7/LockHide-Cursor/. Then 3 errors popped up:

Assets/scripts/Menu.js(24,5): BCE0005: Unknown identifier: 'DrawCrosshair'.

 DrawCrosshair();

Assets/scripts/Menu.js(36,38): BCE0005: Unknown identifier: 'Player'.

 var health = player.GetComponent(Player).Health;

Assets/scripts/Menu.js(47,5): BCE0005: Unknown identifier: 'DrawCrosshair'.

DrawCrosshair();

Here is all of the code:

  // True if the menu is open and mouse is unlocked
 var MenuOpen : boolean = false;
 
 function Start () {
     UpdateCursorLock();
 }
 
 function Update() {
     // Check whether the menu button was released
     if (Input.GetButtonUp("MenuOpen")) {
         MenuOpen = !MenuOpen;
         UpdateCursorLock();
     }
 }
 
 // Called each time the Gui needs to be drawn
  // Called each time the Gui needs to be drawn
 function OnGUI () {
     if (!MenuOpen) {
         DrawHUD();
     } else {
         DrawMenu();
     }
     DrawCrosshair();
 }
 
 function UpdateCursorLock() {
     Screen.lockCursor = !MenuOpen;
     Screen.showCursor = MenuOpen;
 }
 
  function DrawHUD() {
     
     // Get the health from the player
     var player = GameObject.Find("Player");
     var health = player.GetComponent(Player).Health;
 
     // Position
     var left = 10;
     var top = 10;
     var width = 100;
     var height = 25;
     
     // Make a background box
     GUI.Box (Rect (left, top, width, height), "Health: " + health);
     
     DrawCrosshair();
 }
 
 // Draw the menu
 function DrawMenu() {
     var centerX = Screen.width/2;
     var centerY = Screen.height/2;
     
     // location of the menu
     var menuLeft = centerX - 50;
     var menuTop = centerY - 50;
     var menuWidth = 100;
     var menuHeight = 100;
     
     var buttonX = menuLeft + 10;
     var buttonWidth = 80;
     var buttonHeight = 20;
     var buttonDist = 25; // distance between each button
     
     // Make a background box
     GUI.Box (Rect (menuLeft, menuTop,menuWidth,menuHeight), "Menu");
     
     // Start / Resume
     if (GUI.Button (Rect (buttonX,menuTop + 1 * buttonDist,buttonWidth,buttonHeight), "Resume")) {
         MenuOpen = false;
         UpdateCursorLock();
     }
     
     // Restart
     if (GUI.Button (Rect (buttonX,menuTop + 2 * buttonDist,buttonWidth,buttonHeight), "Restart")) {
         Application.LoadLevel(Application.loadedLevel);
     }
     
     // Quit (Only works in the Build. Does not work in the eidtor!)
     if (GUI.Button (Rect (buttonX,menuTop + 3 * buttonDist,buttonWidth,buttonHeight), "Quit")) {
         Application.Quit();
     }
 }