meaning of oetree and oe path to be set while generating pwm.ko

hi everyone!
i was trying to generate pwm.ko file as given on site http://elinux.org/BeagleBoard/GSoC/2010_Projects/Pulse_Width_Modulation. I have installed openmoko toolchain on my pc. The site has a statement OETREE shoulld point to the OE folder? What does this mean? Should i install the OE mentioned on elinux.org?