Date/time formats are used to determine how to display and parse dates, converting between internal representations and text. Dates can be displayed in many ways, and can provide arbitrary amounts of information depending upon the context and the date's semantics. The same patterns can be used to format a value for display as well as parsing text input into numeric values.
Date formatting in Mango is implemented by the SimpleDateFormat Java class, the details for which can be found here. Usage examples can be found therein.
Formatting may be localized depending upon your Java VM defaults.