How do I construct an "Add" routine for a custom object list?

Question

I feel really stupid asking this question, but here goes...

I'm trying to create a custom object in VB, that is itself a list (or collection, or "tuple" - I'm not sure what the difference between these is) of custom objects, and I need to create routines to add and remove these secondary objects to/from the larger custom object. So far, my code goes something like this:

Public Class parameterSet
    Friend _xParameter As String
    Public Property xParameter() As String
        Get
            Return _xParameter
        End Get
        Set(value As String)
            _xParameter = value
        End Set
    End Property
    Friend _yParameter As String
    Public Property yParameter() As String
        Get
            Return _yParameter
        End Get
        Set(value As String)
            _yParameter = value
        End Set
    End Property
    Friend _zParameter As String
    Public Property zParameter() As String
        Get
            Return _zParameter
        End Get
        Set(value As String)
            _zParameter = value
        End Set
    End Property
    Public Sub New(ByVal xParameter As String, ByVal yParameter As String, ByVal zParameter As String)
        _xParameter = xParameter
        _yParameter = yParameter
        _zParameter = zParameter
    End Sub
End Class
Public Class parameterCollection
    Friend _parameterCollection As New List(Of parameterSet)
    Friend Sub Add(xParameter As String, yParameter As String, zParameter As String)
        Throw New NotImplementedException()
    End Sub
End Class

What do I have to put in the Add routine to make this work?