To enable attendance for an event you need to either create an event, or edit an already existing event.

You can choose to enable attendance for an event by checking the "Attendance Enabled" box. From the expanded list you can then choose who will be invited to this event.  You can invite people by their role (selecting the whole group of people with that role), or you can also invite specific people by name.

A note about notifications: Attendance must be enabled in order to send notifications about an event. Notifications are only sent to the users who are invited to an event. Attendance RSVP notifications are sent based on the settings in "advisor" - the module that controls all site notifications.  New event notifications are typically sent within three hours of an event being added and attendance being enabled. They will only receive the invite once, but depending on your advisor settings, they can receive reminders if they fail to respond right away.

Information on advisor settings is available here.

Recipients can answer their RSVP notification from their email client using the links provided without having to login.

They can also RSVP to an event from within the site under "My Events"

To disable attendance for an event, uncheck the attendance checkbox on the edit page of the event, and save your changes.

Enable/Disable attendance from the Master calendar page

Navigate to: Master Calendar 

Select the events you need to adjust by clicking on them, but on on the event name. The row will highlight a pale yellow and blue.

Click the "Actions" button and then select "enable/disable attendance" and follow the on screen instructions.

Please note, if you are enabling attendance this way, to also click "Actions" again and then select "change invited roles" in order to select your attendees, otherwise attendance will be enabled, but no one will be invited.