The "Files" section of the XF86Config file contains the path to
the RGB database file (which should, in general, never need to be
changed), and the default font path. You can have multiple FontPath
lines in your XF86Config; they are concatenated. Ensure that each
directory listed exists and is a valid font directory. If the server
complains about "Can't open default font 'fixed'", it is because there
is an invalid entry in your font path. Try running the 'mkfontdir'
command in each directory if you are certain that each one is correct.
The XF86Config(4/5) manual page describes other parameters that may be
in this section of the file.
Next comes the "Keyboard" section. In this section, you can specify the keyboard protocol (Xqueue or Normal), the repeat rate, and the default mapping of some of the modifier keys. In general, nothing will need to be modified here. Users of non-English keyboards might want to change the definitions of the modifier keys. See the XF86Config(4/5) man page for details.
After this comes the "Pointer" section. In this section you can specify the pointer protocol and device. Note that the protocol name does not always match the manufacturer's name. For example, some Logitech mice (especially newer ones) require either the MouseMan or Microsoft protocols, not the Logitech protocol. Some other mouse parameters can be adjusted here. If you are using a two-button mouse, uncomment the Emulate3Buttons keyword - in this mode, pressing both mouse buttons simultaneously causes the server to report a middle button press.
Note that if the server complains about being unable to open your mouse device, this is NOT a server problem. It has been a very common misconfiguration error on several of the OSs, and 99.999% of the time it is because the device is not correctly configured in the OS. Hence don't bug us until after you prove that your OS level support is correct.