Tic tac toe question using arrays

I am very new to programming and we have recently started into arrays, which by the way, I really don't fully understand at all. We are writing a tic tac toe game in which you have to use an array. I initialized the array and would like to use it to test for a winner, but I have no idea how to go about that? This is a homework assignment and I just need a gentle push in the right direction. Here is what I have so far:

Public Class mainForm
Dim gameBoard(2, 2) As String
Dim playTurn As Integer = 1
Dim letterTurn As String


Private Sub Label1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles box1Label.Click
If playTurn Mod 2 = 0 AndAlso playTurn < 9 Then
letterTurn = "O"
box1Label.BackColor = Color.Orange
Else
letterTurn = "X"
box1Label.BackColor = Color.Yellow

End If
box1Label.Text = letterTurn
playTurn += 1
box1Label.Enabled = False

End If
End Sub

Private Sub exitButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles exitButton.Click
Me.Close()
End Sub

Private Sub newGameButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles newGameButton.Click
box1Label.Text = String.Empty
box1Label.BackColor = Color.Linen
box2Label.Text = String.Empty
box2Label.BackColor = Color.Linen
box3Label.Text = String.Empty
box3Label.BackColor = Color.Linen
box4Label.Text = String.Empty
box4Label.BackColor = Color.Linen
box5Label.Text = String.Empty
box5Label.BackColor = Color.Linen
box6Label.Text = String.Empty
box6Label.BackColor = Color.Linen
box7Label.Text = String.Empty
box7Label.BackColor = Color.Linen
box8Label.Text = String.Empty
box8Label.BackColor = Color.Linen
box9Label.Text = String.Empty
box9Label.BackColor = Color.Linen


End Sub

Private Sub box2Label_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles box2Label.Click
If playTurn Mod 2 = 0 AndAlso playTurn < 9 Then
letterTurn = "O"
box2Label.BackColor = Color.Orange
Else
letterTurn = "X"
box2Label.BackColor = Color.Yellow


End If
box2Label.Text = letterTurn
playTurn += 1
box2Label.Enabled = False


End Sub

Private Sub box3Label_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles box3Label.Click
If playTurn Mod 2 = 0 AndAlso playTurn < 9 Then
letterTurn = "O"
box3Label.BackColor = Color.Orange
Else
letterTurn = "X"
box3Label.BackColor = Color.Yellow

End If
box3Label.Text = letterTurn
playTurn += 1
box3Label.Enabled = False
End Sub

Private Sub box4Label_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles box4Label.Click
If playTurn Mod 2 = 0 AndAlso playTurn < 9 Then
letterTurn = "O"
box4Label.BackColor = Color.Orange
Else
letterTurn = "X"
box4Label.BackColor = Color.Yellow

End If
box4Label.Text = letterTurn
playTurn += 1
box4Label.Enabled = False

End Sub

Private Sub box5Label_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles box5Label.Click
If playTurn Mod 2 = 0 AndAlso playTurn < 9 Then
letterTurn = "O"
box5Label.BackColor = Color.Orange
Else
letterTurn = "X"
box5Label.BackColor = Color.Yellow

End If
box5Label.Text = letterTurn
playTurn += 1
box5Label.Enabled = False
End Sub

Private Sub box6Label_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles box6Label.Click
If playTurn Mod 2 = 0 AndAlso playTurn < 9 Then
letterTurn = "O"
box6Label.BackColor = Color.Orange
Else
letterTurn = "X"
box6Label.BackColor = Color.Yellow

End If
box6Label.Text = letterTurn
playTurn += 1
box6Label.Enabled = False
End Sub

Private Sub box7Label_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles box7Label.Click
If playTurn Mod 2 = 0 AndAlso playTurn < 9 Then
letterTurn = "O"
box7Label.BackColor = Color.Orange
Else
letterTurn = "X"
box7Label.BackColor = Color.Yellow

End If
box7Label.Text = letterTurn
playTurn += 1
box7Label.Enabled = False

End Sub

Private Sub box8Label_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles box8Label.Click
If playTurn Mod 2 = 0 AndAlso playTurn < 9 Then
letterTurn = "O"
box8Label.BackColor = Color.Orange
Else
letterTurn = "X"
box8Label.BackColor = Color.Yellow


End If
box8Label.Text = letterTurn
playTurn += 1
box8Label.Enabled = False
End Sub

Private Sub box9Label_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles box9Label.Click
If playTurn Mod 2 = 0 AndAlso playTurn < 9 Then
letterTurn = "O"
box9Label.BackColor = Color.Orange
Else
letterTurn = "X"
box9Label.BackColor = Color.Yellow

End If
box9Label.Text = letterTurn
playTurn += 1
box9Label.Enabled = False
End Sub
End Class