Upload the plugin folder to the plugins directory, and activate on the plugins page.
In your theme, get the focal point position by calling get_post_meta with your attachment’s $id:
<?php
$x = get_post_meta($attachmentId, "x", true);
$y = get_post_meta($attachmentId, "y", true);
?>The values returned are percentages from the left and top edges of the image, so you can use them in object-position or background-position:
<?php
$focalpoint = "${x}% ${y}%";
…
?>
<img style="object-position:<?php echo $focalpoint ?>">