To create a Card Review, the first thing you need to do is to find in our site the card you are reviewing.
For this, you should visit the section from the main menu. Then you need to navigate to your game, and select the corresponding expansion set, or use the Card Search form.
Once you have found the card in our site, you need to click on its name. You get a pop-up window displaying the details of the card and its image, if available. You will also see a link at the bottom of the card that says 'Write a Review about this card'. This is the link you need to follow in order to create your Review.
Then you need to enter your review title and text into the provided form, as explained here.