need help to understand this code piece

I'll appreciate any comments you can insert to help me understand this code. Many thanks.
 
Protected Sub btnNext_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnNext.Click
    Try
      If Me.chkRecall.Checked Then
        SetCookie("ImmRec", "VaccDetailsRecall", "1")
      Else
        SetCookie("ImmRec", "VaccDetailsRecall", "0")
      End If
      Using cnn As New SqlConnection(oUtil.SQLConnectionString)
        cnn.Open()
        Using cmdD As New SqlCommand(String.Format("DELETE FROM VaccineSelectEdit WHERE UserRecordID='{0} ...