A lot of new users are wanting to use the "what's happening" feature to see what kind of public posts are made on your server. You might want to switch it on?
You can switch it on by going to Preferences > Administration > Site Settings, and tick the box marked "Allow unauthenticated access to public timeline", then click "Save changes".
Also, I would strongly advise you to NOT tick the box marked "Include federated content on unauthenticated public timeline page". All this second box does is fill your "what's happening" page with posts from other people's servers, and it doesn't really help people know what your server is like.