' ===== Paste into the UserForm's code window =====
Private Sub UserForm_Initialize()
    txtDate.Value = Format(Date, "dd-mm-yyyy")
    cboCustomer.List = ThisWorkbook.Sheets("Lists").Range("A2:A5").Value
    cboProduct.List = ThisWorkbook.Sheets("Lists").Range("B2:B5").Value
End Sub

Private Sub cmdSave_Click()
    ' --- validate before writing anything ---
    If Not IsDate(txtDate.Value) Then MsgBox "Enter a valid date": txtDate.SetFocus: Exit Sub
    If cboCustomer.ListIndex = -1 Then MsgBox "Pick a customer from the list": Exit Sub
    If cboProduct.ListIndex = -1 Then MsgBox "Pick a product from the list": Exit Sub
    If Not IsNumeric(txtQty.Value) Or Val(txtQty.Value) <= 0 Then MsgBox "Qty must be a positive number": Exit Sub
    If Not IsNumeric(txtAmount.Value) Then MsgBox "Amount must be a number": Exit Sub

    Dim r As ListRow
    Set r = ThisWorkbook.Sheets("Entries").ListObjects("tblEntries").ListRows.Add
    r.Range.Value = Array(CDate(txtDate.Value), cboCustomer.Value, cboProduct.Value, _
                          CLng(txtQty.Value), CDbl(txtAmount.Value), Environ("USERNAME"))

    txtQty.Value = "": txtAmount.Value = "": cboProduct.ListIndex = -1
    cboProduct.SetFocus
End Sub

' ===== Paste into a normal Module =====
Sub ShowForm()
    UserForm1.Show
End Sub