XWindows is launched with the command startx or init 5 . There are some differences between init 5 and startx but if you don't know which one to choose try startx, because it uses less memory.
An X server can be thought as a driver for graphics cards that the system uses to run GUI. Linux supports lots of graphics cards and you probably won't get trouble with it. If you don't know the chip you have, try to run utilities that comes with your distribution called Xconfigurator , xf86config or something.
The configuration file for your XWindows is at /etc/X11/XF86Config . If Xconfigurator doesn't suit your needs you have to edit it manually. A lot of people have trouble about it. The main reason is the lack of hardware knowledge. It might take a hundred times, but using defaults will usually get you by.
Now, let's discuss some specific problems you may face with about the subject.
It may be boring to type this long command string everytime you launch XWindows. Then make an alias... If you don't kow how to make this refer to my ls tip page and do everything for startx as you do for ls.