Storage is used to store Decorations when not in your Empire.
Moving into StorageEdit
After Store is chosen in the rightmost menu pop-up, you may click on any Decorations in your Empire and they will go into Storage.
Below, Store has been chosen, and the Cow Decoration is about to be moved into Storage.
Moving out of StorageEdit
To bring Decorations out of Storage, use the Build menu.
Look through the Decorations menu and find the Decoration as normal. You will now notice the Decoration has a crate with the number of that Decoration currently in Storage in the upper right hand corner. When you Build stored Decorations, you are not charged.
In this picture from the Build menu, there are 17 horses in Storage. The player will not be charged 60 coins for building any horses until they have first built all 17 currently in Storage.
Able to Move In and OutEdit
Each Decoration moved into Storage increase that item's crate count by 1. Each Decoration built decreases that item's crate count by 1. You will always build the free copies you already have in Storage first. You are able to move items in and out of Storage as many times as you want and they will not be lost. Once the player has built all of that item they had in Storage, they will be charged for building new copies of that Decoration, as normal.
Known Sync delay for Happiness when Moving out of StorageEdit
Sometimes you will have to refresh the game to get the Happiness statistic reset after rebuilding objects that were in Storage.