WordPress.org

1. Unzip biorhythm.zip
2. Upload the folder biorhythm to the /wp-content/plugins/ directory
3. Activate the plugin through the Plugins menu in WordPress
4. Add the plugin to the sidebar through the Appearance/Widgets menu in WordPress
5. Make sure the sub-directory img is writable.

In the folder img the plugin will store the pictures of the biorhythms of your visitors. Each file is about 1.5KB so you will have to cleanup sometimes.