Oracle has a TO_DATE function for converting a date string into the Oracle format, and a TO_CHAR function for converting a date into a formatted string.
Try running the following sql statements to see the differences:
select sysdate from dual;
select to_char(sysdate, 'dd-Mon-yyyy hh24:mi:ss') from dual;
The first one will give you the date in the default format for your system. The second one, you control the formatting. You should be able to find examples of the formatting masks you can use by doing a search on either TO_DATE or TO_CHAR