Well, you should have either WP-DownloadManager or WordPress Download Monitor running in your WordPress installation and you should list at least one WordPress.org hosted plugin or theme in your downloads. My plugin dm4extensions will not hurt your WP site if this is not true, but it would just not do anything in such case.
Upload the full plugin directory into your wp-content/plugins directory.
Activate the plugin in plugins administration.
That's it, the plugin runs automatically in the background via cron. There is no configuration of the plugin.
Requires: 2.8 or higher Compatible up to: 3.2.1 Last Updated: 2011-10-7 Downloads: 1,125