What don't you understand about the JS Fiddle I gave you?
- HTML form,
- CSS to style the form,
- a jQuery function to calculate form input values. jQuery code goes inside <script> tags.
The only other thing you need is a link to the latest jQuery Core Library inside your document's <head> tags like this:
<!--JQUERY CORE LIBRARY-->
<script src="http://code.jquery.com/jquery-latest.min.js">
</script>
Nancy O.