如何使用此Ftp代码

我是新来的c#。我想知道我应该在这个代码中更改什么来连接到我的ftp服务器。有人能帮我吗？我无法理解string fileName、Uri serverUri、long offset，所以请帮助我

ftphost address= localhost
username = test
password = test
filename = test.zip
   public static bool RestartDownloadFromServer(string fileName, Uri serverUri, long offset)
    {
        // The serverUri parameter should use the ftp:// scheme.
        // It identifies the server file that is to be downloaded
        // Example: ftp://contoso.com/someFile.txt.
        // The fileName parameter identifies the local file.
        //The serverUri parameter identifies the remote file.
        // The offset parameter specifies where in the server file to start reading data.
        if (serverUri.Scheme != Uri.UriSchemeFtp)
        {
            return false;
        }
        // Get the object used to communicate with the server.
        FtpWebRequest request = (FtpWebRequest)WebRequest.Create(serverUri);
        request.Method = WebRequestMethods.Ftp.DownloadFile;
        request.ContentOffset = offset;
        FtpWebResponse response = null;
        try
        {
            response = (FtpWebResponse)request.GetResponse();
        }
        catch (WebException e)
        {
            Console.WriteLine(e.Status);
            Console.WriteLine(e.Message);
            return false;
        }
        // Get the data stream from the response.
        Stream newFile = response.GetResponseStream();
        // Use a StreamReader to simplify reading the response data.
        StreamReader reader = new StreamReader(newFile);
        string newFileData = reader.ReadToEnd();
        // Append the response data to the local file
        // using a StreamWriter.
        StreamWriter writer = File.AppendText(fileName);
        writer.Write(newFileData);
        // Display the status description.
        // Cleanup.
        writer.Close();
        reader.Close();
        response.Close();
        Console.WriteLine("Download restart - status: {0}", response.StatusDescription);
        return true;
    }

谢谢Addvance。