Public Structure OrderItem
        Public Product As String
        Public Quantity As Integer
    End Structure
 
    Public Structure Order
 
        Public Sub New(ByVal orderNumber As Integer)
            Me.OrderNumber = orderNumber
            OrderDate = Now
            OrderItems = New List(Of OrderItem)
        End Sub
 
        Public OrderDate As DateTime
        Public OrderNumber As Integer
 
        Public OrderItems As List(Of OrderItem)
    End Structure
 
    Private Sub Test()
        Dim o As New Order(123)
 
        Dim oi As New OrderItem
        oi.Product = "Pink Cucumbers"
        oi.Quantity = 33
        o.OrderItems.Add(oi)
    End Sub

Those people who think they know everything are a great annoyance to those of us who do - Isaac Asimov