Help me with Gui Text

for starters,Score += 10 isn't right..

say :

Score + 10;

but this will just print "Score:10" every time, if you want to accumulate points, you need an int to store the current score:

 var label : GUIText;
 var Score : String = "Score:";
 var currentScore : int;
 
 
 function Update() {
     label.text = Score + currentScore;
 
 }
 
 function OnTriggerEnter(){
 
 currentScore += 10;
 Counter = Score + currentScore ;
 Debug.Log("Get 10 Points!");
 
 
 }

of course, each object with this script has it's own instance of currentScore, so whichever one hits will have its own unique score.. if you want a unified score, you would access a static var:

on player script (named "PlayerScript"):

 var label : GUIText;
 var Counter ="";
 var Score : String = "Score:";
 static var currentScore : int;
 
 function Update() {
     label.text = Counter;
 
 }

on trigger script:

 function OnTriggerEnter(){
 
 PlayerScript.currentScore += 10 ;  // use name of script
 Debug.Log("Get 10 Points!");
 
 
 }

hope this helps EDIT: ok, let me try to clarify:

first off, my mistake, I had put the "static" on the wrong line, it's fixed now; the point is, you need to declare an int (or float) to store numeric data, rather than a string; by declaring the int as static, we are saying this value is universal through all instances of this script. So, if I change it in one place, it changes everywhere. Of course, this won't matter much if the script in question is only used once, and normally it would be just once, on the player for example, which is why I did it that way.. BUT, just declaring it right in the same script would still keep it constant (if static) either way..

 var label : GUIText;
 var Counter : String;
 var Score : String = "Score:";
 static var currentScore : int;
 var myDamage : int = 10;
 
 function Update() {
     label.text = Counter;    
 }
 
 function OnTriggerEnter(){    
 currentScore += myDamage;
 Counter = Score + currentScore ;
 Debug.Log("Get " + myDamage+" Points!");   
 }

here the score is instanced in each object, but the overall score stays static between all objects (if I add 10, it updates every object to the same value)

which is basically what you want I think, just set the var myDamage to 20 on the other object prefab only prob is for performance, there's really no need to be updating the GUIText from EVERY object with this script(though I think it should still work though)..

Better to have one script somewhere drawing the GUIText, and access the int from the script with multiple instances, so in one script on ONE gameobject in the scene:

 var label : GUIText;
 var Score : String = "Score:";
 static var currentScore : int;
 
 function Update() {
     label.text = Score + currentScore;
 
 }

now since currentScore is static, we don't even need an instance of the script to access it, we can just refer to it directly using the name of the script:

 var myDamage : int = 10;
     
 function OnTriggerEnter(){    
 OtherScriptName.currentScore += myDamage;
 Debug.Log("Get " + myDamage+" Points!");   
 }

this should work as seen here :)