WooCommerce Pretty Emails Plugin requires WordPress 3.8+ and WooCommerce 2.1+
Just like every plugins, just copy the woocommerce-pretty-emails folder in your wp-content/pluginsfolder then activate it through WordPress dashboard. The plugin is only accessible for Admin users.
You can also upload the zip file using the WordPress automatic installer.
If the installation went OK, you can now access the plugin Dashboard from the WooCommerce > Settings Menu, Then go to the email tab.