SUDO allows you to execute commands as another user, usually root. I always thought su and sudo were somewhat similar but they are in fact quite different.
SU allows you to switch the user context you are running under just like logging in as a different user.
SUDO will just execute the command you instruct it to as the different user then return you to your usual user rights.
SUDO is a separate program and can be configured by editing the sudoers file (/etc/sudoers)
SUDO allows you limit which commands each user or group can execute so you can use it to give certain groups of user defined admin rights.