Basic idea is pretty simple: to guide boats to port so their cargos can be unloaded in a way that avoids collision (see screen shot above). You direct the boats by drawing with your finger the line it must take to the dock of your choice, and then it chugs away complete with sounds effects and cheery music.
Complications arise when there are more boats than berths ('t was ever thus), boats can only dock in certain berths (ditto), pirates attack (er...), and tornado storms whirl boats around and around (happens all the time).
It's all good fun and enjoyable and there are 6 different maps with selection of charts and complications to work away at.
The only downside is after doing all six a couple of times there's a feeling of "what next?" and it becomes a bit repetitive.
But it doesn't cost that much so worth a punt.