Calculator GUI Help

[Twilikari]

I was practicing my scriting, and I somewhat succesfully FIXED a calculator script. Too some of you, it may look veryyyy familiar. But I wanted to take it one step further. i wanted to make into a fully operational calculator GUI. I've never even attempted to make a GUI however, and I am completely lost. Any help is greatly appreciated!

I'm not looking for someone to do it for me, more of guide me. I want buttons for numbers in the GUI, and some kind of output for the answer.

PHP Code:

function onCreated() {
  temp.a = 2;
  temp.b = 1;
  temp.c = 3;
  temp.a = onAdd(temp.a, temp.b);
  onResult(temp.a);  
  temp.a = onSubtract(temp.a, temp.c);
  onResult(temp.a);  
  temp.a = onDivide(temp.b, temp.a);
  onResult(temp.a);  
  temp.a = onMultiply(temp.b + 1, temp.c);
  onResult(temp.a);  
}

function onResult(temp.result) {
  echo("Result: " @ temp.result);
}

function onAdd(a, b) {
  a = a+b;
  return a;
}

function onSubtract(a, b) {
  a = a - b;
  return a;
}

function onDivide(a, b) {  
  if (b == 0) {
    a = "Error: Can't divide by 0!";
  } 
  if (b != 0) {
    a = a / b ;
  }  
  return a;
}

function onMultiply(a, b) {
  a = a * b;
  return a;
} 


Thank's for the help, in advance! ^~^