WordPress.org

1. In the WordPress admin panel go to Plugins->Add New-> then search for 'claptastic' -> Install the Claptastic Clap Button
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Setup the plugin in Settings->Claptastic Clap Button

If none of that suits you, you can always embed the javascript code anywhere in your theme that you want, in a sidebar widget, in your footer--anywhere you like. Get the latest embed code at http://claptastic.appspot.com/