How do I set up my reference tables?

[DelannaLeonard]

I have a table called Items where I store each item that I ordered. 

Each item has an invoice but each invoice have many items on it so I find myself attaching the same invoice to different items. I don't want to do that.

I want to know how to set up my tables so that these things can happen:

• When I'm in Items table I can add a new invoice/ attach one that is already made.
• When I'm in invoice table I can add an invoice and have an Enumlist of items so that i can choose more than one items to attach to the invoice. 
• I also want the Enumlist to only show items that have not yet had an invoice assigned to it.

Thanks alot for the help in advance.