When you join a world you will be able to search for and find 64 different Easter Eggs. Each easter egg is shaped in different colors and are smaller blocks. All of the easter eggs are placed on the surface so it’s not really impossible to find them all. It’s suggestable to join a regular world with no man made editing made to it because otherwise it can be very hard to find the easter eggs as they may get spawned inside the walls of buildings and so on.
Once you find an easter egg you should break it. What next happens is that the easter egg will drop random items. Not all stuff is especially epic but it’s said to drop diamond gear and other cool stuff.
The Easter Pig can be hard to find so if you can’t find it you should probably go ahead and use the Too Many Items mod to spawn ID 500 which is the pig. The Easter Pig drops eggs which you can place down on the ground which creates an easter egg which you can break to get more random stuff.