Before you go see the Rock in the sequel Jumanji: Welcome to the Jungle, maybe you should see the original 1995 movie Jumanji with Robin Williams. Or maybe you could save the time and just see the new Honest Trailer for it.
The plot is incomprehensible, and the whole premise is based on a board game that doesn't exist, but hey, it's got Robin Williams, so it was a hit. This Honest Trailer doesn't made Jumanji any clearer, but maybe it was never meant to be understood. So go ahead and see the new film, if you're into that sort of thing.