To add a product in Web Commander, go to the Product ribbon and click "Create a product". This will open a popup to enter product details like name, SKU, category, price, and inventory information. You can also add images, videos, attributes, and related products. Finally, add the product to your store pages by dragging a product widget onto the page layout and selecting the products to display. Product inventory can be managed for each product individually by enabling tracking on the product properties page.