In the Invoice Inquiry module you can search for invoices and view what they contain. Invoices are created manually through the "Browse and Adjust Invoices" module. They are also automatically created when a unit possessing inventory charges is sold and those charges are moved from the unit to the seller's Accounts Receivables account.
When you first open the module all invoices will be shown on the left of the page. You can search by invoice number in the search bar. Select the invoice of your choice and it will automatically display its contents.