If you want to add taxes to products / items or invoices you have to configure them on the Taxrates settings page.
To add a new taxrate, click the settings icon
near the right hand side of the main menu, select
Taxrates, and click the
New button near the top right of the page.
First enter the official name of the taxrate. Be careful as this will be displayed on quotes or invoices as a description of the taxrate. Then enter the percentage of the taxrate and click on