whatis and apropos don't work

[Yunus]

Dear All,

I'm using FC3. I tried to issue these commands  below at terminal window:
      [yunus@localhost ] whatis ls      
      bash: ls nothing apropriate              <<== i always get this message
                       and
      [yunus@localhost ] apropos browser
      bash: browser nothing apropriate    <<== i always get this message

Could anyone help me with this problem?

Thanks in advance!

Regards,

yunus