At Admin Panel -> Settings -> Switches, the "article ratings" switch activates a ratings option where visitors can select a number of stars to give a article. The default scale is 1 to 5 stars. If you want a different scale you can customize it at Admin -> Articles -> Article Settings -> "Vote Values". The images used for these stars are templates/images_default/ajaxstar.png, if you want to customize. People can vote simply by clicking the number of stars they want to give the article, they don't need to go to the separate voting page unless the ratings w/comments switch is on.

Admin Panel -> Members -> Manage Usergroups controls who can rate articles.

If you want multiple rating types you can add custom rating fields.

Ratings With Comments

The "Article ratings w/comments" switch is intended for product reviews sites (think amazon.com etc) and will prompt people to type a text comment (like a review) while leaving their rating. A consequence of needing to collect a comment is that the rating images will become static (no longer click-on-a-star-to-rate) and people will have to visit the "vote" page to vote. If this were not the case, the comment couldn't be associated with the rating.

With the ratings w/comments switch on, the voting page automatically gets a list of reviews at the top showing who gave what rating with what comment.

To customize the voting/reviews page, go to Admin -> Themes -> Manage Templates -> Article Templates -> "Vote".