There are three default permission settings when creating a dot.

Share With: Everyone
The Dot will be completely public, anyone who comes to Blue Dot can see it.

Share With: Friends
The Dot can only be seen by your friends.

Share With: Me (Private)
You are the only person who can see the Dot.

Publish dots to a smaller group of friends (to a "Friend List)

1. Click the People Tab.
2. Click My Friends, just below the People tab
   
3. On the right hand side of the page is a box labeled "Organize Friends." Type in a name for the Friend List and click "Create Friend List"
4. Go down the list of your friends and check the boxes next to the names of the friends that you want to include in your Friend List, and click Save Changes.

Now, when you are creating dots, in addition to Everyone, Friends, and Me (private) the name of the Friend List will appear in the Shared With: list. If you choose to share with a friend list, only people in that Friend List can see and comment on those dots.