Как работает конструкция Try - Catch - Visual Basic .NET

Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles    Button1.Click
        Dim a, b, c As Integer
        Try
            a = Convert.ToInt32(TextBox1.Text)
            b = Convert.ToInt32(TextBox2.Text)
            c = a / b
            Label1.Text = c
 
            'Throw New System.Exception("Неверный формат")
            'End Try
            'Try
            '    a = Convert.ToInt32(TextBox1.Text)
            '    b = Convert.ToInt32(TextBox2.Text)
        Catch divideByZeroException As Exception
            MsgBox("Деление на ноль")
            TextBox2.Text = ""
        Catch argumentException As Exception
            TextBox1.Text = ""
            TextBox2.Text = ""
            MsgBox("Неверный формат")
        End Try
    End Sub
End Class