Judging by the helpfully straightforward statement of purpose here at the beginning of the video -- "we're gonna spin him around, see how dizzy he gets" -- we can be certain that these young fellows have at least apprehended the basic purpose of the merry-go-round, although they seem to have grasped it a little late in life. How the trash can got factored into the proceedings is unclear, but it does serve as a foreshadowing of the failure that is about to take place; it's pretty safe to assume that the only person who didn't see this ending in disaster is the guy located inside the trash can.
Poor kid, but it's hard to feel too bad for him, though -- after all, it's this kind of shit that ruined merry-go-rounds for the rest of us.