You’ve created an album containing the best photos of a friend’s wedding. The photos are from various events; indeed, some were emailed to you from other attendees.
You’d prefer that the photos were in an event of their own. Easy. Select the album, choose Edit > Select All, then choose Events > Create Event. iPhoto creates a new event, and moves the photos in the album into the event. Note, however, that the photos are removed from the events where they originated.