To start, stack the box top and bottom to create a base, then place the five wooden rafter pieces on the starting card on top of the base.
On a turn, lift a rafter, place a raft card on the playing area, replace the rafter, then place one of your treasure chests somewhere on the raft...ideally in a precarious position because if someone else knocks off this chest, they must keep it in their hold. If a player collects five treasure chests owned by other players in their hold, they're out of the game! (You can knock off your own chests without penalty, but you're making the game easier for everyone else.)