The gameplay is turn-based combat in which you control the characters indirectly, improving their attacks by tapping the screen at the right time. You'll have to use each of your character's abilities according to the strengths and weaknesses of your enemies and with good timing.
As you advance, you'll level up your crew and be able to upgrade their equipment, recruit soldiers, and improve your stats to go on the new missions that will be given to you.
One Piece Treasure Cruise is a fantastic game for fans of this anime and manga. It is absolutely free, although you can always speed up your progress by purchasing upgrades through the in-game shop.