First, thank you so much for considering helping our WordPress community out by volunteering for the Themes Team.
Reviewing a theme can be a very rewarding experience where you can learn a lot from reading and evaluating other peoples code.
It can also be very difficult, and it can be time consuming.
Last year, we wrote extensive documentation on how to review themes, but we found that very few people read it, and that it was still too much to take in: Especially if you are on a contributor day and have limited time.
That is why we want to make it easier for new contributors to take small steps towards getting started with theme reviews.