From Fedora Project Wiki

Fedora releases since Fedora 10 do not create a /etc/X11/xorg.conf file, used to configure the X server, by default. The X configuration is automatically determined each time X is started. In most cases, this works well and there is no need to manually specify X configuration information.

If you need to make manual changes to X configuration for any reason, you will first need to create a /etc/X11/xorg.conf file. There are several ways of doing this.

system-config-display

Deprecated Package
system-config-display was deprecated during the Fedora 14 development cycle and will not be available in Fedora 14+.

If you have the system-config-display package installed, you can use the system-config-display command to create a configuration file. You can run it interactively simply by running system-config-display as root (or find it in the system menus under System > Administration > Display). This may not work if you cannot run X at all. In this case, you can run it non-interactively by using the --noui parameter, like so:

system-config-display --noui

This will create a clean /etc/X11/xorg.conf file using the automatically detected driver for your video card. If you wish to specify a particular driver for your card you can simply create a standard /etc/X11/xorg.conf file and then edit it by hand, but you can also do this directly with system-config-display. For example, to specify the nv driver, you could do:

system-config-display --noui --set-driver=nv

When using the --set parameters, --noui is implied, so you do not really need to include it. For more information on ways you can use system-config-display, run system-config-display --help.

Xorg -configure

If you do not have the system-config-display package installed and cannot easily install it (for instance, you are stuck without X, and networking is not working), you can create a basic xorg.conf using the X executable itself. As root run:

Xorg :1 -configure

This will create the file /root/xorg.conf.new, which you can then copy to /etc/X11/xorg.conf:

cp /root/xorg.conf.new /etc/X11/xorg.conf

and edit according to your needs.