Private Sub Command3_Click()
List2.AddItem (List1.ListIndex)
End Sub

Option Explicit

Private Sub Command1_Click()
Dim i As Integer, c As Integer

If List1.ListCount = 0 Then
    MsgBox "No items found."
    Exit Sub
End If

c = 0
For i = 0 To List1.ListCount - 1 Step 1
    If List1.Selected(i) = True Then
        c = 1
        Exit For
    End If
Next i

If c = 0 Then
    MsgBox "Please select some items from the list."
    List1.SetFocus
    Exit Sub
ElseIf c = 1 Then
    For i = 0 To List1.ListCount - 1 Step 1
        If List1.Selected(i) = True Then
            List2.AddItem List1.List(i)
        End If
    Next i
End If
End Sub

Private Sub Form_Load()
Dim i As Integer

For i = 1 To 12 Step 1
    List1.AddItem MonthName(i)
Next i
End Sub