communication problem server-multiple clients

My programming knowledge is really low(as much as my english), thus my problems are trivial and hopefully i will receive fast and valuable answers;)

1.At the end this part of my app shoudl be some kind of a server, which is sending and receiving messages from clients. Now its kind of communicator, but works good only when i'm connected with one client. How can I make it good for multiple clients(one my [pathetic;] tries is under "//")?
2.How can I take my IP when I'm using router?
3.How can I make function auto-taking clients IP(not writing it manually)

I'll take any help;)


here's code:

Code:

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public partial class Form1 : Form
    {


        Socket sck;

        EndPoint epLocal, epRemote, epRemote2;

        byte[] buffer, buffer2;


        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            sck = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            sck.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);

            textLocalIP.Text = GetLocalIP();
            textRemoteIP.Text = "10.0.0.5";//GetLocalIP();
            //textRemoteIP2.Text = "10.0.0.3";

            //MessageBox.Show(textRemoteIP.Text);
        }

        private string GetLocalIP()
        {
            IPHostEntry host;
            host = Dns.GetHostEntry(Dns.GetHostName());
            foreach (IPAddress ip in host.AddressList)
            {
                if (ip.AddressFamily == AddressFamily.InterNetwork)
                {
                    return ip.ToString();
                }
            }

            return "127.0.0.1";
        }

        private void btnPolacz_Click(object sender, EventArgs e)
        {
            epLocal = new IPEndPoint(IPAddress.Parse(textLocalIP.Text), Convert.ToInt32(textLocalPort.Text));
            sck.Bind(epLocal);

            epRemote = new IPEndPoint(IPAddress.Parse(textRemoteIP.Text), Convert.ToInt32(textRemotePort.Text));
            sck.Connect(epRemote);

          // epRemote2 = new IPEndPoint(IPAddress.Parse(textRemoteIP2.Text), Convert.ToInt32(textRemotePort2.Text));
          //  sck.Connect(epRemote2);

            buffer = new byte[1500];
            sck.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref epRemote, new AsyncCallback(MessageCallBack), buffer);

          //  buffer2 = new byte[1500];
          //  sck.BeginReceiveFrom(buffer, 0, buffer2.Length, SocketFlags.None, ref epRemote2, new //AsyncCallback(MessageCallBack), buffer2);

        }

        private void MessageCallBack(IAsyncResult aResult)
        {
            try
            {

                byte[] receivedData = new byte[1500];
              //  byte[] receivedData2 = new byte[1500];
                receivedData = (byte[])aResult.AsyncState;
              //  receivedData2 = (byte[])aResult.AsyncState;

                ASCIIEncoding aEncoding = new ASCIIEncoding();
                string receivedMessage = aEncoding.GetString(receivedData);
              //  string receivedMessage2 = aEncoding.GetString(receivedData2);

                take.Items.Add("Friend: " + receivedMessage);
              //  take.Items.Add("Friend2: " + receivedMessage2);

                buffer = new byte[1500];
                sck.BeginReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref epRemote, new AsyncCallback(MessageCallBack), buffer);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }

        private void Send_Click(object sender, EventArgs e)
        {
            ASCIIEncoding aEncoding = new ASCIIEncoding();
            byte[] sendingMessage = new byte[1500];
          // byte[] sendingMessage2 = new byte[1500];
            sendingMessage = aEncoding.GetBytes(write.Text);
          // sendingMessage2 = aEncoding.GetBytes(write.Text);


            sck.Send(sendingMessage);
          //  sck.Send(sendingMessage2);

            take.Items.Add("Me: " + textNapisz.Text);
            write.Text = "";

        }

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