On the live site, you can enable users to subscribe using the Content subscription web part, just as described here. You only need to enable your gateway in the Gateway names property of the web part.
On the live site, the web part displays a check-box for each gateway when multiple gateways are selected. If you enable a particular check-box, the gateway's form is displayed, as you can see in the screenshot below.
Page url: http://devnet.kentico.com/docs/5_5r2/devguide/index.html?using_the_gateway_on_your_site.htm