What is writing a review on SFF:SE? I'm not sure why, but there's a new icon in the top , along with the inbox, reputation, help, and "other sites" icon. It has "queues" for reviews and other things. What are these reviews for?
See What are the review queues, and how do they work? on Main Meta (the Stack Exchange network-wide meta site). The review queues work pretty much the same on Science Fiction & Fantasy as on any other site:
With at least 500 rep, you can review new users' posts to see if any action is required on them (voting, flagging, editing, commenting, etc.) See As a user who is new to the review process, is there a best-practice guide for reviewing first-posts/late-answers? for advice on reviewing in these queues.
With at least 2000 rep, you can review suggested edits from low-rep users and also review flagged low-quality posts for potential deletion.
With at least 3000 rep, you can take part in closing inappropriate or off-topic questions and also reopening closed questions that were closed wrongly or have been edited and improved.
Note that you're not obligated to take part in any of these activities: they are privileges, not responsibilities.