Hi

I'm running an evaluation version of RHEL6.
created a few users and groups using shell but cant get the gui application working.

I have gnome desktop environment installed.
startx runs but in the applications > sys tools menu I have no users app
nor in system menu.
system-config-users is not recognised as a command.

Do I need to install something else before this works?

Alot of the additional functionality like this requires additional packages to be installed.

Since you're in your 30 day evaluation period, you can call RedHat support for help. If you're not planning on paying for RHEL, then before you go too far, remove it and load CentOS instead. Without a paid-for subscription, your server WILL NOT get bugfixes/patches/security updates/kernel patches, and you'll wind up with an unstable system that you can't patch or load new software to, without a good deal of work. Also, the yum package manager won't work, since you won't have access to the Red Hat Network.

Kustom42 gave the right answer..but it will only work during the brief eval period, or if you're paid up.

They don't have to stop right away. There are guides to converting RHEL to CentOS. I've done it before and I know other people who've had good experiences doing it.

Quite true, but unless you pay for RHEL or convert to CentOS, you're going to be out of luck with running yum commands, or pulling things from the online repositories.