Mariculture’s main focus is the Aquatic Environment. It adds terrain generation to the oceans, with things like coral and kelp, to improve the visuals of the underwater world. The mod also expands upon the vanilla fishing system, adding various types of rods and loot you can catch with them, while requiring you to use bait in order to operate these new fishing rods. As well as this, Mariculture introduces fish breeding, which can be a handy way to get your hand on various resources, slowly but surely. There is also jewelry that you can enchant made from pearls, as well as various new objects, that will help with exploring under and above water. Mariculture also adds various machines, that use or create Redstone Flux, with a focus on water related things to power them, or function.
If you are stuck, as long as you have the mod Enchiridion installed alongside Mariculture, you will have books that you can read that will help explain many more indepth things about the mod. The first one will usually be given to you on the creation of a new world. The magic book will be given when you harvest a pearl from an oyster. And the three other books will be given to you, when you craft the following: Iron Wheel, Reed Fishing Rod, and Snorkel.