If you have already enabled sudo for one account, then it is simply a matter of adding the required users to the group, "wheel", or on some distro's it may be "sudo".
If sudo hasn't been enabled yet.
Run "visudo" as root, and uncomment the line (again, this line could be "%wheel"):
%sudo ALL=(ALL) ALL
Which will enable any users in the group "sudo" to run any commands that root can run (so all of them), by entering their OWN password.
has more information for more detailed sudo setups, and only allowing access to certain commands.