Voxpress integrates your wordpress site with the Ubivox newsletter service. Subscribe, unsubscribe, archive lists and much more.
To install the plugin, just copy the plugin directory to you wordpress plugin folder and activate it on the plugins page.
After the plugin has been activated you have to connect it to your Ubivox account by going to the plugin settings page and enter the account URL, the account API url, username and API key.
You'll find all the information inside your Ubivox account under the menu "Account" -> "Users & security" -> API Authentification.