Favouriting an item is great when you want to save an interesting listing to checkout later, or when you would like to compare different options before committing to buying a product.
You will then be able to keep track of any changes (price, location, campaign, status...) as well as saving the product on your profile to quickly find it at any time.
Simply tap on the orange Buengo Heart on the bottom right of the item image on your item feed or on the item screen. Tap again to unfavourite it.
To find your favourited items, go to your profile screen and under the "Items" tab, tap on "Favourites". Tap on any listing to see the details, and tap on the Buengo Heart.