You might want a community for only a select group of family members to see your children’s pictures. Selecting a community type of private and restricted means only you, and those you specifically designate, can either view or submit posts and comments. (Why you don’t want to share pictures of your beautiful children with the world, and to allow random people to comment how cute they are, is a discussion for another day.)
Later that day (based on our indirect prodding), you change your mind and decide to share those beautiful pictures with the world. You just don’t want anyone to be able to comment or post pictures of how much more beautiful their children are. (Clearly, this is a made-up example, as what kind of parents would try to one-up each other… right?) A restricted community is then the best choice. You can still limit who can post or comment, but anyone can see the pictures.
Public is what you might expect. As with the sidewalk, anyone can walk on it. As long as you’re not banned from doing so. A community moderator can ban individual users or domains from a public community as they find it necessary (e.g., spamming). Please don’t be the one to make it necessary.
We’re not entirely sure it’s appropriate to call this the Frequently Asked Questions area as, candidly, we don’t keep track of how often these questions get asked. Consider this community as a place where we post answers to what we anticipate your questions will be. But, if our crystal ball is malfunctioning, feel free to post your question in /GettingStarted/Help. If we turn your question into an FAQ, we’ll credit you back the karma to post it. It’s the least we can do. We also welcome suggestions at /GettingStarted/SuggestionBox.