When you create e.g. an invoice then you can specify the unit used on each invoice line, e.g. hour, week, item. You create the units by using the menu item Settings -> Units.
Enter a name for the unit that is used internally within the administration program.
Here you can select a language and then provide language dependent information that the user will see in e.g. the webshop.
Enter a name for the unit for each supported language.
Enter an abbreviation for the unit for each supported language.