Adding Products in the Shopify Admin Dashboard
If you are looking to upload and add new products within GemPages' application, it is unfortunately not possible. The only way you can add and customize your products will be to reach your Shopify Admin Dashboard.
Step 1: If you are on GemPages' dashboard, move over to your Shopify Admin Panel (accessible through this link: your-store.myshopify.com/admin), and locate the Product section on your left sidebar.
Step 2: Open it and you will see the list of all the products already inside your store. Just click on "Add Product" on the top right of your page.
If you don't have any products, click on "Add Product" in the middle of your page and you will be redirected to a new page where you will be able to modify every aspect of your product.
Kindly follow this complete tutorial from Shopify's HelpCenter if you need specific answers regarding to adding your products.