All you have to do is embed this little HTML snippet in your page and a comment box will appear there.
<script src="https://apis.google.com/js/plusone.js"></script>
<div id="comments"></div>
<script>
gapi.comments.render('comments', {
href: window.location,
width: '624',
first_party_property: 'BLOGGER',
view_type: 'FILTERED_POSTMOD'
});
</script>
This what you'll see on your website.