If you need some help with getting creative for fish or coral, have a look at the photos in this folder. I have chosen this photo as a guide to begin my creation and will refer to and use tools as needed.
I used the brush tool. I'm gonna change the colors to suit my taste.

I will create a new layer and find another coral and continue with my scene.

Here is what I have created so far...
Save your work.
What is next? Let me look at some photos and work others have done to decide the next layer. I used my imagination and help from others and completed my background scenery. It is much better to create each plant on a separate layer so that later you can intermingle the fish. Notice the layers and their names. They can be moved around so that one plant or fish is in front of another plant or fish.