This is the first star related achievement in the game and will likely come within the first group of levels. You can get a maximum of 3 stars per level so the minimum amount of levels you will have to play is 17.
If you need help on any specific levels this website is great for tricky levels.
http://www.cuttheropewalkthroughs.com/You'll need to keep playing and earn more stars to unlock the following:
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