You at your boat. It's a sad, boring little boat. Certainly not good enough to help you travel the world. The only way to improve it is to go adventuring and recruit some new blood. You do that by matching tiles, of course.
If you've played 10000000, the basics of You Must Build A Boat will come naturally. Your character runs along the top of the screen and you've got a game board below that. You have to match the tiles to trigger the right actions to keep him running along. Monster? Match some swords or staves. Locked chest? Match keys. You have to be fast or you'll be knocked off the screen and the run is over.
By completing quests and making it farther, you'll get new crew members to improve your boat. That in turn helps you improve your abilities. It's ridiculously engaging, just like the previous game, and there's enough new gameplay that it feels like a legitimate upgrade. Does it sound like I'm gushing a little? I guess I am. This is a crazy-fun game, and it's only $2.99 with no in-app purchases.