Right of you've only got a single joycon then the controls are rotated as you hold it sideways. You press L and R at the same time to let the system know what you're using as a controller.It was confusing because they had 4, two of which were connected resembling a normal controller and the other 2 were split apart. Then one of the split apart ones were supposed to be used.
I'm surprised they'd have a demo set up with only one joycon though.
Anyway, wasn't able to try it out enough because of this. Played a bit of Smash in the Nintendo store tho with my gf until she gave up