The easiest place to rate images is the Library View. This is because you can compare images to each other. In the Library View, there are many different options to rate your images either by using your mouse or with keyboard shortcuts.
In the Gallery View, you can flag and rate a photo directly on the image thumbnail. When you hover your mouse over a thumbnail that is unmarked, a small outline of a heart and five stars appear along the bottom edge.
To start:
Now you can apply ratings directly to the image.
TIP: Using your mouse to rate images. If you right click on an image, a drop-down menu will appear. At the top of the menu will be Set Flag, Set Rating, and Set Color Label. Once selected the type of rating, a second set of options will be available specific to that rating type, letting you flag or reject an image, rate it from 1 to 5 stars, or apply a color label.