i have a network of rh9 most of servers connected locally and another servers connected through internet
I just want to know how can i use vnc to connect remotely to any desktop of any server in the network because we use some software that may have some problems and i want to see what happens to it and then start the software on this server

Red Hat 9 reached its "end of life" in 2004 so "some software may have some problems" is probably an understatement.

Sorry I could not be of specific help with your VNC. Recommend that you contact redhat.com and purchase an upgrade immediately if you are interested in running secure and stable servers!

Also, you may want to look in to installing a VPN on one of your servers. A VPN would allow secure access to your LAN so you could VNC into any server without much hassle.

I know rh9 is so old but the company work on some software that run on it so no problem about rh9
And there some applications already came with rh9 like remote desktop connection ,vnc server , Xvnc and vnc viewer.
When i tried to read the man pages for them and other discussions on the web i couldnt get any thing .

You'll have to go through the install media for RH9 and try anything that looks likely.
As above, its so old that current stuff (almost definitely) won't talk to it.

I already installed vnc viewer ,Xvnc ,vncserver and remote desktop connection from installation media
But they are many programs with many commands and options
And i found it confusing because i didnt know what should i use first and what can be used together and how

VNC is a tool used to connect to remote Unix machines & provides a GUI rich desktop session on the remote machine. But as far as I am concerned, use of VNC inside a Linux box is only when you want a graphical desktop of the remote server. Else, you can directly connect to the remote server using a terminal from your local server. VNC is mainly used by Windows based machines to access Unix environment.

-- ADD ---
In order to access a remote desktop session, you'll first need to install VNC server on remote machine. Then you can create a VNC port for yourself on that remote machine and using that port no. you can connect to the remote server from your local machine though VNC Viewer.

What you use depends on what you want. There are many good tutorials available, so I won't repeat them here. Here's one: http://www.skullbox.net/vncserver.php. Note, however, that VNC is rather insecure, so you should use RH9's firewall to block incoming VNC connections and use SSH tunneling to connect.

i installed a realvnc and when i tried to make connection i got this message
Authentication failed
Exception failed to connect: Connection refused (111)

then i installed NX and also when i tried to make a connection i got this message
session NUMBER failed
The remote proxy closed the connection while regonitiating the session. This may be due to the wrong authentication credentials passed to the server.

Are you running a VNC server on the machine you're trying to connect to? There needs to be a server running on the remote machine that you're trying to connect you.

Also, I don't think you understand just what a risk it is to be running Red Hat 9 -- there have been NO SECURITY patches released for it since 2004. If you're running any service exposed to the outside world, you are pretty much inviting every cracker on the Internet to take control of your infrastructure, which is probably not what the owners of your business want. Can the app you run seriously not run on anything more modern than RH9? RHEL or one of its free derivatives (e.g. CentOS) would be a good choice.

i already installed vnc server on the remote machine .
and i know that rh9 is so old but there is no choice to me for that but fortunately there is connection to the outside world, and we can't run our apps. over RHEL or CentOS because of many things the most important of them is the kernel

Check the firewall on the server, it needs to allow connections to port 5900 to VNC directly into the machine. If you're running an SSH server, then it's much safer to use an SSH tunnel to connect.