FVWM: how can i get the fvwm start?

[ch huang]

i use centos5.3,now my desktop is xfce,and i have installed fvwm
./configure
make
make install
and everything is fine.but, now question is how can i get it start?
i switch to console 0 ,and type init 3 to stop my xfce,and type fvwm (also
tried fvwm2) ,get an error: can not  display
how can i do to make fvwm work?