Trigger enabling keys

At the moment I have a trigger to make a menu pop up saying that the person won the level. Then i want them to be able to press a key to conitnue to the next level. However I'm not really sure how to do it.

I currently have:

function OnGUI () {   
 GUI.skin = mySkin;
if (triggerEnd == true)     
GUI.Label (Rect (Screen.height-300, Screen.height-125, 200, 100), "Fortress Annihilated!", "TextField"); 
//insert key code here
};

Your code looks good. Add braces after your if statement to enclose the GUI and the part you are about to add. After the GUI.Label(). Add:

if(Input.GetKeyDown(KeyCode.Space)) {
Application.LoadLevel(/*Next Level*/);
}

So your whole code will look like this.

function OnGUI () {   
    GUI.skin = mySkin;
    if (triggerEnd == true) {     
        GUI.Label (Rect (Screen.height-300, Screen.height-125, 200, 100), "Fortress Annihilated!", "TextField");
        if(Input.GetKeyDown(KeyCode.Space)) {
            Application.LoadLevel(/*Next Level*/);
        } 
    }   
}