I think I get it now. Here's my sudoers file:
# This file MUST be edited with the 'visudo' command as root.
# See the man page for details on how to write a sudoers file.
Defaults passwd_timeout = 1
Defaults timestamp_timeout = 5
Defaults listpw = all
Defaults verifypw = all
Defaults lecture = always
Defaults loglinelen = 0
# Host alias specification
Host_Alias HOMEMACH = MYHOMEPC-HP-PC
# User alias specification
# Cmnd alias specification
# User privilege specification
root HOMEMACH=(root) PASSWD:ALL
alec HOMEMACH=(root) PASSWD:/sbin/shutdown
# Allow members of group sudo to execute any command
# (Note that later entries override this, so you might need to move
# it further down)
%sudo HOMEMACH=(root) PASSWD:ALL
# Members of the admin group may gain root privileges
%admin HOMEMACH=(root) PASSWD:ALL
so, what you're saying is: in this specific case, a user named foo would have no sudo rights, because I did not mention him?
And I figured out alot of the rest on my own, through trial and error (with the original default /etc/sudoers backed up, modifications done on a LIVE usb)..
but there are one or two more questions I still have.
-I see a lecture=always default exists, but can I customize this lecture?
and thank you so much tuxboom!! =)