[newbie] fsck(file system check)

[chronos]

Hi all,
Wanted to know how do you run fsck ( file system check ) ? I just 
reinstalled both my os`s and wanted to clean up through my linux partition. 
I read in the man pages that your supposed to unmount your drives or 
something. I just wanted to know how to do it correctly.
                                                                                       
                               Thank 
you, Chronos.