Select the products you wish to add to the order; the process is the same as with the Clients, if you want to remove one of the items from the order, just tap it and hold it, the option to remove will show up. You can also filter the list of products that are In-stock, or that are On-sale. Filter off will display all products. There are also options to search by code, name or category.
After selecting a product, enter the quantity. When you tap on the quantity field, a numeric tab will appear to help you. Do this for every product you add.