Here's a list of presentations submitted to your event in response to Call for Proposals.
At the beginning presentations are marked as "pending" and they wait for your action. You can then mark them as accepted, rejected or votable. You can also publish them (only after publishing they will be visible on your event page). Once marked, you can browse them in specific groups.
Grades, comments and labels
Presentations can be marked with grades by organizers and reviewers (checkout out "Group Memberships" to find out more about reviewers).
You can also add comments to presentations and mark them with labels. Click the presentation's name and you will get there.
Slides and videos
You can add slides and videos to the presentations. Choose "Upload slides" and you will get there.