Creating Calculator Using AppendDigit And Else If Functions?

I am new to Java and my teacher goes way too fast in class and am a day behind on this calculator. Our assignment is to make a Calculator using AppendDigit and Else if functions in the java code. Some of my other code in html may be messed up as well. I am just lost so here is the HTML:

Code:
<title>John's Calculator</title>
<style type="text/css">
.rt {text-align:right; font-family: Courier New;}
.numbttn {text-align: center; background-color:
silver; font-family: Courier New; width 4eM;}
body {background-color: silver} .....

And Here is the pathetic Javascript which I have barely started:
Code:
// cal Applet- John Falco- 20 October 2010
function clear TB() {
document.form.kpd.display.value="0";
}
function AppendDigit (x) {
if (x==".") {
if ((!HasDecimal))
}
else {
document.forms.kpd.display.value =
document.forms.kdp.display.value + X;
};