Collect the Eggs is a limited time event that gives boosters as rewards for collecting eggs that are hidden in bubbles of levels.
When the event becomes available, you'll see an event button on the map screen. Tapping the event button will open the event info screen from which you can see how many eggs you have collected, the rewards you receive by reaching the collection targets, as well as a timer that shows you how much time you have left to collect the eggs.
How to play the event?
During the event, you'll see bubbles with eggs on them in the levels. Popping those egg bubbles will drop eggs that then get added to the egg counter.
During gameplay in level, you see an egg counter placed beside the bird character in the bottom left corner of the game screen. The counter shows you how many collectibles you have collected in the level.
At the end of the level you presented with the level summary screen. A quest widget will show your current progress towards the next event milestone. Any eggs you've collected are added to your total.