You can use both weapons to kill the different creatures that will try to take your life. At the beginning, there are only jellyfish, but it won't be long before you're running into sharks and other dangers.
But it's not only marine creatures that you need to be careful of. You also need to watch how deep you dive, since going too far will cause the pressure to break your diving suit. And in that case, of course, it's game over.
FarSky is an exploration game with a really special atmosphere composed by excellent graphics. Some moments, like when kelp forests are swaying around your head, or enormous schools of fish are surrounding you, are truly spectacular.