Fill out the three pages fully to create the event successfully, click "Submit" and the event will then appear on your Dashboard under "My Upcoming Events" and for any schools that have approved your Organization.
What are My Preferred Organizations? You can post an opportunity to a specific school by selecting it as a "Preferred Organization". You can do this in the Manager tab in the Outgoing Opportunities page.
See this video on Posting an Opportunity to Students for Non-Profits: https://www.youtube.com/watch?