Welcome to the CentOS fora. Please see the recommended reading for new users linked in my signature.
You have given us no idea what you want to do, so it is virtually impossible to offer any specific advice.
If you want to use GUI tools you will need an X server, or use VNC
. Alternatively you might use a web interface such as Webmin
In any case, your provider should not be suppling an obsolete, insecure, and unsupported release, and should be providing at least some guidance. 5.7 is the current release. See the CentOS 5.7 Release Notes