Display a Text/GUI on screen when triggerd with Fadein/Fadeout

Unity GUI is a little complicated if you're new to scripting, so take your time learning it. It will eventually all make sense. :-)

For size, you'll probably want to use a GUIStyle, and set the fontSize.

See: http://docs.unity3d.com/Documentation/ScriptReference/GUIStyle.html

For fading, you'll want to set the text color's alpha value. For example, with a regular label, this is GUIStyle.normal.textColor.

The example below draws the text at font size 20, with 50% transparency.

     var alpha : float = 0.5;
     
     var style : GUIStyle;
     style = GUI.skin.label;
     style.fontSize = 20; // Set size of text to 20.
     style.normal.textColor = new (1, 1, 1, alpha); // Set color to white w/alpha.
     GUI.Label(new Rect(Screen.width * 0.5f - 50f, Screen.height * 0.5f - 10f, 
         100f, 20f), message, style);

(Warning: untested code above, plus my apologies in case I accidentally snuck some C# code in there out of habit.)

I recommend using a coroutine to handle fading in and out. A coroutine is a function that runs semi-independently from the main loop.

See: http://docs.unity3d.com/Documentation/ScriptReference/index.Coroutines_26_Yield.html

When fading in, the coroutine can change the value of alpha from 0 (completely transparent) to 1 (completely solid). Then OnGUI() can draw the label using the current alpha value.

 function FadeIn(duration : float) {
     if (duration > 0) {
         var startTime = Time.time;
         var endTime = start + duration;
         while (Time.time < endTime) {
             var elapsed = Time.time - startTime;
             alpha = (elapsed / duration);
             yield;
         }
     }
     alpha = 1;
 }