Three secret stars are located throughout each quest for you to collect. 2 of the stars are hidden in secret areas of each quest, so be sure to explore the whole environment! Also, remember that each weapon has a battle ability and an exploration ability. So explore and learn the uses of each weapon, you never know what cool stuff you’ll find!
You also gain 1 star in each quest for finding and killing the donut minions. Sometimes, you won’t be able to get stars in certain levels until later when you have the correct weapon. But remember, you can always re-visit quests to obtain stars that you may have missed!