You can quickly add line items to a Purchase Order via CSV.
Click on Import via CSV located towards the top right of the window.
This should open the importer pop-up;
Create a simple CSV file which contains the details of the order information that you need to import.
Open Excel or any other spreadsheet software and create two columns, SKU and Quantity. Enter the appropriate SKUs and Quantity values under these columns.
Once you've done that you're ready to upload the file to QuickBooks Commerce. Go back to your browser and add the file to the importer.
Click on Import and your data will appear on the order sheets.
Your notes will appear on the documents you send to your Supplier.
Similarly, you can do it on Sales Order. Here's a handy guide for your reference.