有关NameValueCollection的代码，求解释

最近看代码看到一小段代码，硬是没看懂，各位亲们，请指教
private UdpClient client;  
private IPAddress groupAddress;  
private int localPort;  
private int remotePort;  
private int ttl;
private IPEndPoint remoteEP;
try
  { 
  NameValueCollection config = ConfigurationSettings.AppSettings;
  groupAddress = IPAddress.Parse(config["GroupAddress"]);
  localPort = int.Parse(config["LocalPort"]);
  remotePort = int.Parse(config["RemotePort"]);
  ttl = int.Parse(config["TTL"]);
  }
  catch
  {
  MessageBox.Show("读取文件错误！");
  btn_start.Enabled = false;
  }

哪里不懂?就是读取键/值对
http://msdn.microsoft.com/zh-cn/library/system.collections.specialized.namevaluecollection.aspx

获取config中AppSettings所有的键值对
NameValueCollection config = ConfigurationSettings.AppSettings;
获取某个键值对的值，键值名为GroupAddress
  groupAddress = IPAddress.Parse(config["GroupAddress"]);
  localPort = int.Parse(config["LocalPort"]);
  remotePort = int.Parse(config["RemotePort"]);
  ttl = int.Parse(config["TTL"]);

NameValueCollection
就是键值对，Request就是这样的