hmm..go fly is long gone as a company... they were purchased by JAKKS and the Go FLy part got wrapped up and shelved...probably got some old stock....
the easy answer is that you just wrap the velcro around the long spars while holding two boxes next to one another....
with box kites that are identical you can have some fun with the configuration of them too...
you can set them up in the V formation.....
you could set them up so that all three are side by side in a flat orientation....
you could stack them one on top of another....
these last two versions would make you have to fit a simple bridle...good to learn......
you can get some ideas of configurations to play with by searching for Buffalo Box Kites (sadly Dan's company is long gone but you can find some amazing pictures of set ups he did)

picture swiped from F-flying
btw where are you located?