The plugin includes an opt-out feature to exclude certain virtual hosts from being served with Varnish. It also includes a feature to exclude certain URLs from being excluded from Varnish. The Vhost+URL feature however combines both the vhost and URL exclude feature in a nice a easy way to use. So for example if I needed to exclude http://www.unixy.net/secure from being served with Varnish, I would enter the following and submit:
www.unixy.net/secure
Notice how I stripped the "http://" prefix from the URL. The remaining construct of the URL can remain as is.