Guess the Word GUI help

Question

Hey I'm having trouble completing this program. I need to check the users letter guess when they hit the guess button. 

Here's what I have so far:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;


namespace GuessAWord
{
    public partial class Form1 : Form
    {
        int randomNumber;
        Random ranNumberGenerator;
        string ranWord;
        string[] words;
        const int MAXWORDS = 10;
       




        public Form1()
        {
            words = new string[MAXWORDS];


            ranNumberGenerator = new Random();


            words[0] = "dog";
            words[1] = "cat";
            words[2] = "fish";
            words[3] = "bird";
            words[4] = "elephant";
            words[5] = "tiger";
            words[6] = "lion";
            words[7] = "snake";
            words[8] = "walrus";
            words[9] = "owl";


            InitializeComponent();
        }


        private void startButton_Click(object sender, EventArgs e)
        {


            randomNumber = ranNumberGenerator.Next(0, 10);


            ranWord = words[randomNumber];


            mysteryLabel.Text = "";


            for (int i = 0; i < ranWord.Length; i++)
            {
                mysteryLabel.Text += "*";
            }


            feedbackLabel.Text = "";
            guessButton.Enabled = true;
            userTextbox.Select();


        }


        private void guessButton_Click(object sender, EventArgs e)
        {
           
           
                    }
                }
            }