It is pretty straightforward. At the beginning, press the right arrow key to choose your starting color of beta. Press 's' to hide the crab. When you click on the fish, it sells it, when you click on the food, it feeds it, and when you click the heart you breed them.
I am not completely done with this and I have a few bugs in the store and the cleanliness factor for some reason is not working. I will keep working and reshare when the bugs are fixed. Enjoy for now!