Thanks for using Sitefinity.
Right now we have not implemented a rating system in Sitefinity (I'm guessing you saw the tables for it). It is tentatively in the works but not accessible via the UI or API and we don't have a hard release date for it yet. However, you can use a third party control or develop your own using the module builder for the time being if it is a requirement.
Sorry for the confusion.
I would avoid using it as the property is going to change upon actual implementation and isn't currently supported. Right now we have no supported rating system for products but there will be one in the future. Sorry for the confusion.