If you want to add products with different variants (eg. Color and size), is sufficient when you add a Product, to select Properties, then what you want (Color, size, etc.) and fill out the information for each combination. (If you added in size L and XL and colors black and white, you will have 4 product variants - L - black, XL - black, L - white and XL - white). It remains only to add them a price (the same for all or different) and you will now have 4 different versions of this product.