Socket programming- client server principles

I'm embarrassed to even ask this question, but after an exhausting search in google (starting to have MSDN...), I've decided to post it:

Just now started learning client-server programming (using C#), and trying to write my first code using tcpClient. I'm writing both the server side and the client side. here's my question: Constantly, the client sends one String to the server, and then the server sends a String back to the client and so forth. Can't the server send 2 Strings in a row? he has to wait for the client response? is this the principle of client-server??

Once again, sorry for the lousy question. Thanks...

<> I'll try to post some of my code (a long one...). I tryed to cut the redandent parts, so hope the code makes any sense... (i marked the main problam with //*********)

public class MServer2
{
Dictionary<String, String> nameAndPass = new Dictionary<String, String>();
Dictionary<String, List<String> > nameAndMail = new Dictionary<String, List<String>>();

public static void Main()
{
    new MServer2();
}

public MServer2()
{
    TcpListener server = new TcpListener(8500);
    try
    {
        server.Start();
        Console.WriteLine("started " + server);
        while (true)
        {
            TcpClient client = server.AcceptTcpClient();
            Console.WriteLine("connection accepted " + client);
            new Server1(client, nameAndPass, nameAndMail);
        }
    }
    catch (Exception e)
    {
        Console.WriteLine("exception" + e);
    }
    finally
    {
        server.Stop();
    }
}

class Server1
{
TcpClient client;
NetworkStream netStream;
Dictionary<String, String> nameAndPass1 = new Dictionary<String, String>();
Dictionary<String, List<String>> nameAndMail1 = new Dictionary<String, List<String>>();

internal Server1(TcpClient client, Dictionary<String, String> nameandPassFromFile, Dictionary<String, List<String> > nameAndMailsFromFile)
{
    nameAndPass1 = nameandPassFromFile;
    nameAndMail1 = nameAndMailsFromFile;

    this.client = client;
    Thread thr = new Thread(new ThreadStart(Run));
    thr.Start();
}

public void Run()
{
    try
    {
        netStream = client.GetStream();
        StreamReader reader = new StreamReader(netStream);
        StreamWriter writer = new StreamWriter(netStream);
        writer.AutoFlush = true;
        Console.WriteLine("beginning to receive loop");

        writer.WriteLine("Choose your user name.");
        strFromClient = reader.ReadLine();
        userName = strFromClient;

        writer.WriteLine("Choose your user password.");
        strFromClient = reader.ReadLine();

        password = strFromClient;

        writer.WriteLine("Do you want to see the list of email addresses? (y/n)");
        strFromClient = reader.ReadLine();

//***********************************************************************************
//HERE'S MY PROBLAM:
//HERE THE CLIENT WILL GET A STRING SHOWING HIS EMAILS, AND I WANT HIM TO GET ANOTHER     STRING ASKING "Do you want to add an email address? (y/n)", BUT IT LOOKS LIKE THE SERVER     "WAITS" FOR A RESPONSE FROM THE CLIENT TO SHOW THE NEXT STRING...
        if (strFromClient == "y")
        {   
            String tmpStr = null;
            List<String> tmp = nameAndMail1[userName];
            for(int i=0; i<nameAndMail1[userName].Count; i++)
            {
                tmpStr += tmp[i] + " ";
            }

            writer.WriteLine(tmpStr);                            
        } 
        writer.WriteLine("Do you want to add an email address? (y/n)");
        strFromClient = reader.ReadLine();

    }    

}
    catch (Exception e)
    {
        Console.WriteLine("{0} Exception caught.", e);
    }

EDIT VOL 2

OK! After 2 hours of misery, I think I found the problam thanks to Phil Frost (the genius!) --- the problam is probably in the client... (Im souch an a-hole!).

The server does send 2 string in a row, but my stupid implementation of the client side doesn't show a message (which recived from the server) that doesn't follow a message sent by the client...

So once again I need your help. Here's a view of how I designed the client form:

My lack of experience led me to connect to the server when the "connect to server" button is pressed, and only when the "send Message" button is pressed, a message from the server is desplayed. The problam is when 2 (or more) messages from the server are recived without sending a message from the client to the server- the client doesn't know that a new message is recived! Where do I suppose to recive the messages from the server? ('where' means under which function, for example- right now it happens in the sendMessage_click function).

thanks again for all the help so far!!