Hi:
put an .xinitrc file in your home - that's the quickest you can do.
Usually the xinit files are located in:
 /usr/X11/lib/X11/xinit (X11 is a link to X11R6)

But that depends on the setup of the server at compilation time.
For quick startup you might use:

---<Snip> -----------
#!/bin/sh
exec /usr/X11/bin/xterm &
exec twm
---<End> -----------


This is my .xinitrc (note, that I'm using fvwm):

---<snip here> ------
#!/bin/sh
# $XConsortium: xinitrc.cpp,v 1.4 91/08/22 11:41:34 rws Exp $

userresources=$HOME/.Xresources
usermodmap=$HOME/.Xmodmap
sysresources=/usr/X11R6/lib/X11/xinit/.Xresources
sysmodmap=/usr/X11R6/lib/X11/xinit/.Xmodmap

# merge in defaults and keymaps

if [ -f $sysresources ]; then
    xrdb -merge $sysresources
fi

if [ -f $sysmodmap ]; then
    xmodmap $sysmodmap
fi

if [ -f $userresources ]; then
    xrdb -merge $userresources
fi

if [ -f $usermodmap ]; then
    xmodmap $usermodmap
fi

# start some nice programs
xsetroot -bitmap /usr/X11/include/X11/bitmaps/gray

# To run twm: exec twm
exec fvwm

-<end of .xinitrc>---------------------------------

Regards,
Angel Orille