1. Add the items in your Accounting System.

2. Go to The Order Exchange Item Details page

Menu >Item > Item Details 

at the bottom of the grid, there is a blue Refresh Items button. Please click on that and it will bring all the items from the Accounting System to The Order Exchange.

3. For the items that have barcodes, please click on Edit button next to the item or alternatively you can just double click on the item itself, this will open the Edit Form where you can add the Alternate Barcodes.

Click on Update to save the Alternate Barcode.

4. After adding new items, you need to update the Items Retailer Codes section. For that please see this article

https://theorderexchange.freshdesk.com/a/solutions/articles/35000177905