By default all date and date time fields will attempt to read the user's regional setting that are passed in by the browser. Further information can be found here. This setting will override the default behavior and all users will be presented with the same date format. This setting will only affect on instance of the date or date time field and will not affect report rendering.
To build a new format simply type out the format that you would like to see using the special part markers where you want the different date parts to appear. For example the US date format would be {m}/{d}/{Y} and would output something like 03/05/2014.
Day of the Month {j} - Day of the month without leading zeros, E.g. 1 to 31.
Day of the Month with Leading Zero {d} - Day of the month, 2 digits with leading zeros, E.g. 01 to 31.
Day of the Week {l} - A full textual representation of the day of the week, E.g. Monday through Sunday.
Day of the Week Abbreviated {D} - A textual representation of a day using three letters, E.g. Mon through Sun.
Month Name {F} - A full textual representation of a month, E.g. January through December.
Month Name Abbreviated {M} - A short textual representation of a month using three letters, E.g. Jan through Dec.
Month with Leading Zero {m} - Numeric representation of a month with leading zeros, E.g. 01 to 12.
Year 4 Digit {Y} - A full numeric representation of a year using 4 digits, E.g. 1999 or 2003.
Year 2 Digit {y} - A two digit representation of a year, E.g. 99 or 03.