umask?

[Jay Paulson]

I have been messing around with file permissions on my SuSE box and 
found that the umask needs to be changed in order for files that are 
created in a directory to have group writable permission on them, 
otherwise they are set to not writable for the group.  However, in my 
search to find an explanation of how umask works with all the different 
ways you can set it (022, 002, 0022, 0002, and more I'm sure) I haven't 
found anything that really explain what it does.  Therefore, I'm a 
little bit lost on what to do.

Can anyone point me to a good resource for umask?

When you set the umask can you set it for a certain directory and it's 
sub directories or is it system wide?

Are there any security risks for setting the umask to 002? (Whatever 
that actually does :-] )

Thanks for any help!
jay