A proxy server is a computer that offers a computer network service to allow clients to make indirect network connections to other network services. A client connects to the proxy server, then requests a connection, file, or other resource available on a different server. The proxy provides the resource either by connecting to the specified server or by serving it from a cache. In some cases, the proxy may alter the client's request or the server's response for various purposes.
SYNCING.NET usually detects your proxy server and set him immediately on Configuration-> Options-> Connections. If your proxy server is detected, you can change the proxy settings on this screen.
If you do not know your proxy settings, please contact your administrator.