We have URL filtering features available if you're using one of our Routers, otherwise you would want to use the Firewall options in the User Profile of the SSID to block access to certain sites.
If you are using one of our Routers, this guide reviews how to use the URL filter: http://docs.aerohive.com/330000/docs/help/english/ng/Content/gui/configuration/configuring-router-url-filtering-rule.htm?Highlight=URL%20filtering
