Every session moves through the same states. You'll see them on the Sessions screen.
Scheduled. Players are asked from six days out. Their answers come in as they arrive, and you can open the session and start a draft schedule whenever you like.
Review. RSVP has closed. Check attendance: record late changes, add a guest, note anyone only there for part of the night. Work through the advisor's suggestions, adjust the nets if you want to, then Publish. Players see their evening the moment you do.
Published. Changes you make after publishing are held as unpublished changes until you Republish. Only the players affected are notified.
Live. The session goes live at its start time by itself. Use the schedule for interruptions and changeovers, and End session when you're done.
Done. Attendance is kept as part of each player's history.
Cancelling
From the Sessions screen, cancel the session. Everyone with an account is told immediately, its nets are released for other sessions, and it can't be undone. If plans change, add a once-off.