iTunes 
Rate songs and other items
You can assign a rating to a song, album, video, podcast, or other item to indicate how much you like it. You can use ratings to help you automatically create playlists or to sort and browse your library.
To display the rating column for songs or albums, choose View > View Options, and select Rating or Album Rating.
Assign a rating
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Select the item you want to rate, and click or drag in a rating column to add or remove stars.
When you rate an album, all of its songs are given the same rating. You can change the rating of each individual song. If you rate songs but not the album, iTunes displays the rated songs’ average as the album rating. Stars that iTunes assigns are hollow; stars that you assign are solid.
You can also add ratings by Control-clicking an item and choosing Rating.