i know how to use it !!1
you can find it in enities-editors
and it is a small box
press C on it to edit it
and then type the URL and press ENTER
and then bablaldblal to try to edit below numbers
then you will see the map...
and look at it and then ,
put your blocks or props to build it...
so all its use is only help show the pic in the gmod with XYZ axis
..in fact i think it is a little useless
(just test by myself ,maybe there are other things i am not sure)