In different levels (or in special screens) there are "hidden" golden eggs. Once you touch or see them, they will be displayed in the "Golden Eggs" screen. When you touch them there you can play an extra level
Examples on where to find golden eggs:
- At the end of the credit (just let them running through)
- Just touch the sun in the level select screen
- Complete all of the Worlds in Episode 1 with 3 Stars (same for episode 2)
- If I remember correctly there is also a golden egg "hidden" in the help-section where the "Bomber-Birds" are explained
- In one level there is chest beneath a mountain, just tap it once to get your golden egg
- In other level there is a golden egg at the top right of the screen (only visible when zooming out). There you need a "yellow bird" to reach touch it in order to get your egg.
Make a search on Youtube for "Golden Egg Location", there are many videos showing the exact locations for each of them.
EDIT: This may also be a duplicate of How do you get the golden eggs in Angry Birds?How do you get the golden eggs in Angry Birds? :)
