The Role you select here is automatically assigned to people when they register online for this event (usually the default 'Attendee' role).
You can also allow people to choose a Role by creating a Profile with the Participant Role field. Then include that Profile when you configure the Online Registration page for this event.
When enabled, links allowing people to share this event with their social network will be displayed (e.g. Facebook "Like", Google+, and Twitter).
Social media links will be included on the Event Info page, Thank-you page, Tell-a-Friend page (if enabled), and in event confirmation emails.