Host:
If you are just accessing SABnzbd from the pc it is running on, you can leave it as "localhost".
If you want to access the web interface from other PC's you can:
* Leave it blank to have it automatically find your external IP
* Enter in your machines local ip address if you know it
* Enter "0.0.0.0" to listen on all interfaces including Localhost (recommended if you are having problems)
Web username and password:
If you want to secure the web interface from prying eyes, set a username and password here (warning this is only simple authentication). When you next restart SABnzbd you will be prompted for the username and password before you can use the web-ui.