The roaming document explains adequately how to setup... at least the principle of it.
It isn't hard at all..
One device is the main router.. You create a wireless network from this router.
All other devices are bridged.. (that is router bridge not wireless bridge)
They all get IP address from the main router.
All of them create a wireless network..
if you want roaming you simply use the same name SSID (wireless name in apple speak).. same security setting WPA2 Personal = WPA2 AES and password.
But you can setup different networks if you want.
Channels are supposed to sort themselves out automagically.. but I don't believe in voodoo.. try voodoo first and if it fails, no biggie.. set manual wireless channels.. set simple short names no spaces pure alphanumeric.
It is perhaps new for you and the lack of html setup is a pain.. but it isn't hard to do. Apple have cut back the number of options to barest min to do the job.
Come back and ask specific questions if you run into trouble. We have some very clued up people here.. who spend their life energy answering the same question every day with a cheerful attitude.. never seen the like.. on a windows forum you would be told to RTFM.