Naccount.Accounts itself is not a List you can add to, it's a property you can assign a (reference to a) List to (m_Accounts is a List you can add to but it's private and not yet instantiated (created)).
Your code seems not very useful but this example might help you solve your problem:
Dim Naccount As New ListOfAccounts
Naccount.User = "James"
Dim AccountList As New List(Of Account)
For i = 0 To 5
Dim AccountL As New Account
AccountL.Active = True
AccountL.CreatedDate = Now
AccountL.Email = "james" & i.ToString & "@example.com"
AccountList.Add(AccountL)
Next
Naccount.Accounts = AccountList