Every user, upon registration, is automatically added to two (2) groups: this one, and one titled "Public (All Followers)". You may remain in this group as long as you'd like to network and meet new people to follow. Please do not use this group for "branded" content.
Your Public (All Followers) group is where you will post to your followers. It is not necessary to add users to the group - everyone who follows you will see whatever you post there (as well as things you post in any other public group).