To rate your meals, you'll need to be logged in to your account. Start by clicking "Customize Menu" in the top right of your toolbar menu. On the lefthand side of your screen, click to "Review your meals."
By giving a meal a frowning face, you will be less likely to receive this meal in the future. To ensure you never receive this meal again, make sure to check the box in the pop out that says "Don't send me this meal again". By giving a meal a smiley face, this makes sure the meal will always be available to you when it hits the menu.
Us and our chef partners monitor all of these ratings to make sure our meals are meeting our customer's standards.