To get there, you'll need to start by crafting prismarine sticks out of two prismarine blocks in the way you would craft normal sticks out of wood. After that, craft the prismarine wand with two sticks and one prismarine block along a diagonal:
Use the wand to light a prismarine portal.
There are four biomes in Aquatia: the Aquatis Mountains, the Bubble Forest, the Crystal Spikes and the Soaked Forest. Each have their own unique blocks and mobs.
The Aquatis Mountains is home to new types of fungi (currently useless, but could feature in a new update), the Drowned Creeper, a blue version of a creeper (acts the same) and a Drenched Spider (again acts just the same, only it is blue).
The Bubble Forest has a new wood type, Bubble, which can be crafted into the normal things. It also has Bubble Chickens.
The Crystal Spikes is a huge expanse of ice with spikes of crystal, which comes in three colours: normal (white), pink and blue. When destroyed, they drop white, pink or blue stained glass respectively.
The Soaked Forest has Soaked wood and Drowned can spawn.
Soaked and Bubble fences and fence gates use prismarine sticks instead of the normal sticks alongside the relevant wood planks.
Aquatia currently has two ores, Aqua and Amethyst. Both can be found under Y Level 20 and can be crafted into tools (with prismarine sticks) and armor. They both need to be mined with at least an iron pickaxe and can mine the same level of blocks as diamond.
Apart from these things, there is also an additional bonus item, an invisibility cloak. When worn, you and the cloak cannot be seen and there are no effect particles. It can be crafted like this:
It can also be mended with leather.
There's not many mobs currently so that will be coming in a future update, as well as uses for the fungi and possibly some new biomes. Enjoy!