You wish to hunt fish with a spear? Why, it's as easy as breathing under water. And considering you're not blue in the face, I can tell you will master this skill in no time at all.
First, you will need to search for where fish gather. When you've found a suitable school of fish, steady your spear and strike with a quick and fluid thrust.
That, in a clamshell, is the art of spearfishing. Of course, these explanations mean nothing if you have no spear to practice. Here, take one of mine.
If you look around, you're like to find promising prey close by. Farewell, friend, and happy hunting.