Do difference. Some people ferment in buckets, some in plastic or glass carboys. Carboys look like large bottles.
They probably included the carboy to use as a "secondary fermenter". This is something most brewers don't do anymore. We used to transfer the beer from the first fermenter (i.e., your bucket) to a second fermenter, leaving as much of the bottom trub behind. We did this in an effort to make our beer as clear as possible. Turns out, if you just leave it in that first fermenter, it will also clear up (might take a little longer).
My suggestion to you is just use that carboy as one fermenter and the bucket with the airlock as the second fermenter and do two batches at the same time.