IMPORTANT: All your attendees will become automatically members of your community (they can opt out) if you assigned the event they registered to, to your community. Content wise, a new Forum Category will be automatically created to import your event conversations to the community. With these two strategies, we get an increasing community with very little effort as you leverage your own events (attendees and content).
Go to main menu and click on Communities, then “Create Group”, add your basic information, create categories for the Forum and Blogs areas and start promoting your community. Read post “Shall I create one or more communities? How to grow it?”