sudo command - run command as root

sudo su - open a root shell

sudo su user - open a shell as user

sudo -k - forget sudo passwords

gksudo command - visual sudo dialog (GNOME)

kdesudo command - visual sudo dialog (KDE)

sudo visudo - edit /etc/sudoers

gksudo nautilus - root file manager (GNOME)

kdesudo konqueror - root file manager (KDE)

passwd - change your password