When creating sessions in Eventsforce, sessions can have a status of "Draft" or "Published". By default, each session will be marked as "Draft". A draft session can be previewed by an admin but will not appear to attendees.
Attendees will only see "Published" sessions in your event. This allows further control of the agenda display.
Publishing sessions
Sessions can be marked as "Published" on an individual basis, or in bulk:
Go to Setup > Program > Sessions
Select one or multiple sessions (hold "CRTL" or "Command" to select more than one session)
Click the 'Tools' dropdown
Select "Publish sessions..."
On the popup window, select "Yes"