When you create a discussion, it will, by default, be private. To make your discussion visible to all users on the site, you will need to publish your discussion. Note that you must be the owner of a discussion, or an Admin, in order to publish a discussion. Publishing your discussion will not allow users to make edits to your discussion without being granted specific edit rights - they will have the rights of a Viewer (see: Participant Rights and Roles).
To publish a discussion, go to the discussion menu (click on the three horizontal bars at the top-left of the screen), and select ‘Discussion Settings’. Select the ‘Invites & Permissions’ tab. Under ‘Visibility’, click ‘Publish Discussion’.
Note that once a discussion has been published, it cannot be unpublished or archived (see: Archiving a Discussion). If you have a special need to make a discussion you have published private, please contact support.