It Girl's collections give out fashionable rewards
When you enter a store in It Girl, a window will popup that shows you what your progress is on that store's collection. Each store has a certain number of clothing items that you have to discover in order to get a reward. There are two rewards available, one for simply 'discovering' the clothing, and other for buying all of the items. This is almost exactly the same mechanic that you see in games like Treasure Isle - searching for clothing takes energy, and you can find collectibles. The only difference is that the collectibles you find are wearable if you actually purchase them, and you get actual prizes for completing collections other than simply coins and XP.
What are you waiting for? Start collecting in It Girl!