People you've invited to your activity have three options for responding: Yes, No, and Maybe. They can change their response until the activity begins.
You'll be notified whenever someone responds to your invitation.
Everyone invited to an activity can see who's responded Yes, No, or Maybe, as well a list of people who haven't responded. As the activity organizer, you also have a dashboard to keep track of responses and transactions (web only).
Select the Activities tab and choose your activity. Here you can track the RSVPs, transactions, and adjust details.