Load a Level on Touch

I am new bee in Unity, so please forgive me my silly question. Actually i want to load a Scene while running app. I wrote following code to load scene when i touch texture.

function Start()
{

}

function Update()
{
var hit : GUILayer = Camera.main.GetComponent(GUILayer);
var hitObject : GUIElement = hit.HitTest( Input.mousePosition );

if( hitObject != null )
{
    switch( hitObject.name )
    {
        case "HowToButton":
        print("Touch On How To button");
        print("Load Level Name :"+ Application.loadedLevelName);
        //Application.LoadLevelAdditive ("HowTo");
         Application.LoadLevel("HowTo");
            break;
        default:
            break;
    }
}

}

So when i run on device(iPhone), i couldn’t load HowTo screen and give me this message. “Level ‘HowTo’ (-1) couldn’t be loaded because it has not been added to the build settings.
To add a level to the build settings use the menu File->Build Settings…”
I also added this into scene, but i don’t where i am doing wrong. Please help me. Thanks in Advance.

Salaam , Fortunately, the answer is very simple …

Look in menu File. Open the Build Settings.

You must drag all the scenes you need to that area. Here’s a picture…

Hope it helps. Cheers!