You'll need to decide on a "source" designation. I'd suggest using the friendly URL "slug" for the guide, formatted in a way to make it easily read. The list blow includes examples.
On the guide(s) where you plan to use the widget, add this code snippet to the "Guide Custom JS/CSS":
<script type="text/javascript">
// This tells the Assessment Widget the source of ratings, please don't delete!
var clickSource = "Placeholder Source";
</script>
replacing the text Placeholder Source with the designation you came up with in part 1.
Add a new box to your guide, but choose the "Reuse Existing Box" option. Choose "Clayton's Sandbox" for the guide and "LibGuide Rating Widget" for the box. Please leave it as a mapped box and don't create a copy! That way it'll be easier to manage.
Also, I'd advise changing the box to a Floating Box after you add it to your guide. This is a checkbox that appears if you click the little pencil to edit the box in your guide.