I'm trying to set up an instructions menu that shows when pressing "P" on the keyboard

I was hoping someone could check over my code here, tell me if I'm going about this the wrong way. If so, what would be a better way to tackle this. I'm fairly new to coding and am trying to use the search functions, but I'm at a point where I believe I've looked at this code too much and am having issues.

Assets/Instructionsmenu.js(8,46): BCE0005: Unknown identifier: 'isPaused'.

Assets/Instructionsmenu.js(26,16): BCE0005: Unknown identifier: 'guiSkin'.

Assets/Instructionsmenu.js(29,97): BCE0005: Unknown identifier: 'nativeVerticalResolution'.

Assets/Instructionsmenu.js(29,139): BCE0005: Unknown identifier: 'nativeVerticalResolution'.

Assets/Instructionsmenu.js(32,8): BCE0005: Unknown identifier: 'isPaused'.

 function Update()
 {
  
      if(Input.GetKeyDown("Instructions") && !isPaused)
    {
       print("Paused");
       Time.timeScale = 0.0;
       isPaused = true;
    }
    else if(Input.GetKeyDown("Instructions") && isPaused)
    {
       print("Unpaused");
       Time.timeScale = 1.0;
       isPaused = false;    
    } 
 }
  
 function OnGUI ()
 {
  
     // Set up gui skin
     GUI.skin = guiSkin;
  
     // Our GUI is laid out for a 1920 x 1200 pixel display (16:10 aspect). The next line makes sure it rescales nicely to other resolutions.
     GUI.matrix = Matrix4x4.TRS (Vector3(0, 0, 0), Quaternion.identity, Vector3 (Screen.height / nativeVerticalResolution, Screen.height / nativeVerticalResolution, 1)); 
  
  
     if(isPaused)
     {
       //RenderSettings.fogDensity = 1;
       if(GUI.Button (Rect((Screen.width)/2, 480, 140,70), "W to walk forward", "button2"))
       {
          print("W to walk forward");
       }
       if(GUI.Button (Rect((Screen.width)/2,560,140,70), "S to walk backwards", "button2"))
       {
          print("S to walk backward");
       }
        if(GUI.Button (Rect((Screen.width)/2,560,140,70), "D to walk to the right", "button2"))
       {
          print("D to walk to the right");
       }
        if(GUI.Button (Rect((Screen.width)/2,560,140,70), "A to walk to the left", "button2"))
       {
          print("A to walk to the left");
       }
        if(GUI.Button (Rect((Screen.width)/2,560,140,70), "Left Mouse button to Fire Rifle", "button2"))
       {
          print("Left Mouse button to Fire Rifle");
       }
       if(GUI.Button (Rect((Screen.width)/2,640,340,70), "Back to the game", "button2"))
       {
          print("Back to the game");
          Time.timeScale = 1.0;
          isPaused = false;   
       }
    } 
  
  
 }
  
  
 @script AddComponentMenu ("GUI/Pause GUI")