WordPress.org

1. Unzip into your /wp-content/plugins/ directory. If you're uploading it make sure to upload the top-level folder. Don't just upload all the php files and put them in /wp-content/plugins/.
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Visit your Chennaicentral options (Options - Chennai Central) for WordPress 2.3.x, (Settings - Chennai Central) for WordPress 2.5.x, 2.6.x, 2.7.x, 2.8.x That's all folks!

If you have to upgrade manually simply repeat the installation steps.