Before creating the material, you will have to create the Measurement unit for different types of materials.
To create a new material, go to the "Standard material list" and click the "New material" button (or simply hit N on your keyboard):
Enter the material title, measurement unit, price per unit (excl. VAT) and serial number/material code before clicking "Save".
You can always edit a material. However, if the rate or vat was changed, do not forget to mark a checkbox for updating all template jobs related to a standard material.