TV Tropes Reviews is a special section of the wiki where you can review certain things.
Reviews are available for any page on this wiki that's described as a "work" or a "creator". To access the reviews, either go to such a page and click on the hyperlink that says "x reviews" or go here.
Everything else you need to know is explained when you click on the "add a review" and "about reviews" buttons. However, if you plan to write a review, please think it out well before submitting it. Try to avoid putting up nothing more than a rant explaining how horrible you think something is.