To use an ability simply tap on the decoration then select the "ability" button to apply this. Depending on the ability, there may be a second step to select a butterfly like when applying an aesthetic ability, or laying an egg from a butterfly etc. Aesthetic abilities last a limited amount of time and not all decorations have abilities. Abilities have a cooldown period after use where they will need a little rest before you can use them again. The cooldown length is displayed in the decor information.