The Review Committee is a key part of the conference organization. Its role is to review and comment on submissions, thus providing the input to the Program Committee which makes the final decision on which submissions are accepted and rejected.
The review process is handled through a dedicated software http://pkp.sfu.ca/ocs/ which has been adapted to the specific needs of the European Turbomachinery Conference. Being Reviewer means that you have already registered in the Conference Data Base. The papers you have to process have been attributed to you by the Review Organizer, and you should have been notified of this assignment by Email.