• Go to the Catalogue tab
• In the products section at the top of the page, click on the + button
• Complete the fields for GTIN, product name and product group
  • The GTIN field does error validation so that you cannot upload an invalid GTIN
  • For the product group field you can either select an existing product group you have already created by clicking inside the product group box, or you can type in a new one to create along with the product
• Click on the "OK" button

If you have previously set up your product attributes and packaging components see this article in the Help Centre.