I am not sure how to directly answer your question, but you could look for howto's and tutorials on the web.
A good documentation site to skim through is http://tldp.org
Linux moving forward has mostly dropped XFree86 and has embraced X.org's version.
X is a major part of Linux (from a GUI standpoint) and you should start understanding Xorg.conf. This is the major configuration file.
I am not really sure if this answers your question, since you gave so little information. Maybe a more detailed explanation will give you more help.