Show/hide GUI Texture

Hi, I've got a problem with showing GUI textures. In my game's main menu, when I click the How to play button, I want it to show a GUI texture which tells how to play the game. I'm not a programmer so making scripts is kind of a new thing to me. Anyway, here's my script:

var isHowtoButton = false; var GUITexture = false;

function OnMouseDown() { renderer.material.color = Color.green; if ( isHowtoButton ) { guiTexture.enabled = true; } }