The Catalogue appears in the portal if you have the activity section enabled within the event setup in Xperios. This can be found in the Details tab of the event itself.
The Catalogue details the specifics of the event. For example it has a description of what the Event is, lists who the event is aimed at (audience) and the minimum requirements.
The Catalogue brings these tabs from Xperios together into a cohesive and informative summary that is displayed on the portal when enrolling.