SQL & PL/SQL

Hi,
I have been searching for hours to solve this problem.
I can´t convert a date to only year, month or day etc...



select sysdate, TO_DATE(sysdate,'YYYY') from dual
ORA-01830: date format picture ends before converting entire input string
01830. 00000 - "date format picture ends before converting entire input string"




select sysdate, TO_DATE(sysdate,'MM') from dual
ORA-01843: not a valid month
01843. 00000 - "not a valid month"


select sysdate, TO_DATE(sysdate,'DD') from dual
ORA-01830: date format picture ends before converting entire input string
01830. 00000 - "date format picture ends before converting entire input string"

Please, if this is not the right category to post in just address me to the right one.
Thanks,