The /etc/X11/xorg.conf file tells the X server what kind of
monitor,
video card and mouse you have. You must create it to tell the
server what specific hardware you have.
You'll need info on your hardware:
The recommended way to generate an xorg.conf file is to use the
xorgcfg utility. The xorgconfig text utility is still there
for the (few) cases where xorgcfg can't be used. Also, there is a
sample file installed as /usr/X11R6/lib/X11/xorg.conf.eg,
which can be used as a starting point.
For details about the xorg.conf file format, refer to the
xorg.conf(5) manual page.
Once you've set up a xorg.conf file, you can fine tune the video
modes with the xvidtune utility.
X11R6.8.1 has support for the mouse driver included in
the new wscons console driver introduced by OpenBSD-2.9.
Specify ``wsmouse'' as the protocol and
``/dev/wsmouse0'' as the device in /etc/X11/xorg.conf
if you're using OpenBSD-2.9 or later with a PS/2 or USB mouse.
See README.mouse for general instruction on mouse configuration.