Help me pls

how can i run this javascript code. i must use form variable a[] and b[] :(

<SCRIPT LANGUAGE="JavaScript">

function a_times_b(form) {
a=form.a.value
b=form.b.value
c=a*b
form.ans.value=c
}


</SCRIPT>



<FORM name="form">
<input name=a[] type=text value=12 size=4>
&nbsp;&nbsp;&nbsp;X &nbsp;&nbsp;
<input name=b[] type=text onKeyUp="a_times_b(this.form)" value=3 size=4>
=
<input name=ans[] type value=0 size=9>


</FORM>

You must use square bracket notation. Link here: http://jibbering.com/faq/faq_notes/square_brackets.html

i am not good coder :( i dont understand javascript.
can u help me this coding