If you don't use the acquisitions module or batch load enhanced on order records, you need to manually create placeholder items in order for patrons to place holds.
Use fake barcodes which include your library code, and have somewhere to record where you are in the sequence. i.e. MPL1000, MPL1001, MPL1002
Use ON ORDER as your call number.
Use Evergreen’s On order status for the item record.
Have an On Order holdings template for cataloguers to use.
Create and use an ON ORDER shelving location, especially if your library uses a new book shelving location.
When the item comes in you will need to update the item record.
For further information see the Sitka Cataloguing Policy - http://docs.libraries.coop/policy/_cataloguing_procedures.html#_working_with_on_order_item_records