To add a product start by using the side menu and clicking Products/Services.
You will then be taken to the products page:
Here insert the name of your product and how much you are charging for the product, then click save and you will be taken to this page:
Here you may edit the details of the product by using the blue edit button on the right, or you may use the buttons near the bottom of the page to either add another client, create a quotation, send an invoice or update your settings.