When you download an app from the iOS or Mac App Stores, you have the ability to then go back to the store and leave a review. Here is how to get to the review form. There are also some general guidelines you may want to follow when writing a review. Make sure you review the app, not the App Store system. If the app isn't the one you wanted, don't review the app based on your misconception. Also take price into consideration and don't use the review process as a way to get support from the developer.