The Network Sharing option found within the application is used to enable or disable sharing for folders and applications. It's not used to share the Internet. To share your WiFi connection, install an application developed exactly for this type of process I recommended accessing the database of Software Informer in order to download one. I personally recommend Connectify Hotspot, but if you want something free, simply access the database I've mentioned here. The link will lead you to a search result list that contains only the applications for this request.