At Admin Panel -> Settings -> Switches, the "topic ratings" switch activates a ratings option where visitors can select a number of stars to give a topic. The default scale is 1 to 5 stars. If you want a different scale you can customize it at Admin -> Topics -> Topic 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 topic, they don't need to go to the separate voting page unless the ratings w/posts switch is on.

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

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

Ratings With Posts

The "Topic ratings w/posts" switch is intended for product reviews sites (think amazon.com etc) and will prompt people to type a text post (like a review) while leaving their rating. A consequence of needing to collect a post 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 post couldn't be associated with the rating.

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

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