ok lets say that your making a script that when something happens health goes down by 1 and you want to access it from another script. You write:

transform.Find("Player").GetComponent("Health").health -= 1;

Replace Player with the name of the game object the script is attached to. Health with the name of the script and health with the variable in the script. Hope this helps

First you must know where is your script, it can be in another object or in the same object where you want to access the extern variable. After you need to get the script object using the command GetComponent( ScriptName ). In the following example I am accessing a function from a script called "CounterManager". So I find the objecct that has it, I find the script inside the object, and finally I access the function. You can access the variable exactly like a function. I do not recommend you to access directly variables from other scripts, since you can change then without perceive, and you become crazy to debug it. Use getX() and setX() functions to manage variables externly.

var counter : GameObject = GameObject.Find( "Counter" );
if ( counter == null )
{
    Debug.Log( "StageGUI can't find the Counter object "); 
}


counterManager = counter.GetComponent( CounterManager );

//Setting values - accessing a function from another script
scoreValue.text = ""+ counterManager.getScore();