To submit reader reviews, you first need to sign up for a free user account. Once you are signed into your account, there are two ways you can submit revews:
Click "Submit" on the bar near the top of most pages of the site, then choose the system on which the game appears and the individual title you wish to review.
Browse the site until you find the profile page for the exact game you want to review, then click the "Submit a review of this game" link that appears on that page (near the top, below the information box and any available screenshot gallery).
Either way, you'll arrive at a form where you can enter your review text, a tagline and a rating. Make sure to follow all submission guidelines reflected on that page. Once your submit your review, it will be placed in queue for site staff to look over before it goes live on the site. Assuming your review meets all requirements, it should be approved and appear on the site within a day or two of its submission. Sometimes, reviews will appear much sooner than that!