Tapping is a game mechanic which is used in many ways across the game.
Single Tapping Edit
Floating objects Edit
Gathering Products Edit
Objects all can be tapped for their products.
Opening Chests Edit
Consuming Stars Edit
Collecting Objects Edit
Currency, Magic Gems, Blessing Orbs and Bonus Points all need to be tapped in order to gather them. Higher levels of those objects (with Bonus Points as an exception), however, will have a Tap Confirmation Message when they are tapped (if that option is turned on in the Settings), and when that message (or the button on the lower left hand side) is tapped, they will be collected.
Double Tapping Edit
Harvesting an object can be performed by double tapping the object. If any Creature is available and free (not sleeping or doing something else which it autonomously chose to do) it will come and harvest the wanted object.
Quadruple (4x), Sextuple (6x) and Octuple (8x) Tapping Edit
Some harvestable objects can have more than one Creature harvesting them at the same time. When such an object is present, it can be quadruple tapped for calling two Creatures to harvest it. If three Creatures can harvest at the same time, a sextuple tap can be made to call all three. If four Creatures can harvest at the same time, a octuple tap can be made to call all four.
Tap Protection Edit
In the game's Settings there's an option called "Tap Confirm". When this option is turned on, when tapping a valuable consumable object, an alert of "Confirm Tap?" appears above the object instead of gathering it. After tapping the "Confirm Tap?" button, the item is gathered. It applies to high levels of Currency, Blessing Orbs, Magic Gems, Magic Stars, event points objects and various Chests.
In short, this option prevents accidental unwanted taps on valuable items.