Upon the game's release, you need to 3-star each level available. There are two episodes available (with more to come, most likely):
Episode 1:
60 Normal levels
5 Wall of Pigs levels
1 Bonus levels
Episode 2: 60 Normal levels
4 Wall of Pigs levels
1 Bonus level
This achievement might become easier to obtain once more episodes release. If you are having difficulty with a particular level I would recommend finding a video guide on YouTube. It would be impractical for me to link them all here, but I'll throw up a link to the YouTube walkthrough playlists from which you can find each individual level guide:
Episode 1:
https://www.youtube.com/playlist?list=PLlJklkizbjsbjdlDF49IF...Episode 2:
https://www.youtube.com/playlist?list=PLlJklkizbjsYTrwcS3L3X...