The red decorations tab is the second tab in your aquapedia with the little coral icon. It has information and an image gallery with each different decoration/coral you have discovered.
Each are categorised into sets and you can also see the silhouetted decorations that you are yet to discover! Tap on a coral for more info on its rarity, coin/food production or special ability, cooldown time and to buy any corals with splashcash or purple tickets.