WordPress.org

1. Upload bttl.php to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Go to the 'Design' then 'Widgets' menu to add it to your sidebar. Change the default options in the Widget menu if you like.

Do make sure the path to bttl.php is /wp-content/plugins/bttl.php with no extra directories in between.