To generate a link that will allow anyone who follows it to join a discussion as a Writer, 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 ‘Discussion Writer Invite Link’, click ‘Enable’.
Note that this link can be turned off at any time. You can only turn on this link in discussions that you’re an Admin or Owner for.
Alternatively, you can invite new participants directly. For more information on this option, see Inviting Participants to a Discussion.