Waiting for user input before proceeding with next for statement

public partial class Form1 : Form
{
    Button[] alphaButtons = new Button[26];
    char[] charsToSay = new char[10];
    char letterChoice;
    int charIdx = 0;

    public Form1()
    {
        InitializeComponent();

        int asciiCode = 65;
        for (int i = 0; i < alphaButtons.Length; i++)
        {
            alphaButtons[i] = new Button();
            //add the button control to the form
            this.Controls.Add(alphaButtons[i]);
            alphaButtons[i].Size = new System.Drawing.Size(20, 32);
            int prevIdx = i == 0 ? 0 : i - 1;
            alphaButtons[i].Location = new Point(
                alphaButtons[prevIdx].Location.X + alphaButtons[0].Width, 10);
            alphaButtons[i].Text = Convert.ToChar(asciiCode).ToString();
            alphaButtons[i].Click += new EventHandler(AlphaButtons_Click);
            asciiCode++;
        }

        GetRand();

        letterChoice = charsToSay[charIdx];

        Play();
    }

    private void Play()
    {
        SayLetter();
    }

    private void GetRand()
    {
        // change randomness as desired

        Random rand = new Random();

        for (int i = 0; i < charsToSay.Length; i++)
        {
            charsToSay[i] = Convert.ToChar(rand.Next(65, 90));//ascii chars A - Z
        }
    }

    void AlphaButtons_Click(object sender, EventArgs e)
    {
        Button b = sender as Button;
        char c = Convert.ToChar(b.Text);

        if (c == letterChoice)
        {
            //correct
            MessageBox.Show("Congratulations that is Correct!!!");//test
        }
        else
        {
            //incorrect
            MessageBox.Show("Sorry that is incorrect!");//test
        }

        //you may want to wait a second or two before saying next char
        // i.e. Thread.Sleep(2000);
        //just depends on what you want

        charIdx++;
        if (charIdx < charsToSay.Length)
        {
            letterChoice = charsToSay[charIdx];
            Play();
        }
        else
        {
            // GAME OVER
            MessageBox.Show("GAME OVER!");//test
        }
    }

    private void SayLetter()
    {
        string c = letterChoice.ToString().ToLower();
        SoundPlayer sound = new SoundPlayer(
            @"http://cafe.bevocal.com/libraries/audio/female1/en_us/alphabet/" + c + ".wav");
        sound.Play();
    }
}