How to change channel posting permission levels and discovery options
Channels have two main permission settings: discovery and posting & commenting permissions. Channel editors and owners can change the permissions from the channel settings.
Discovery:
Set the discovery option for this channel. By default the discovery is restricted.
Restricted (default) - Not visible in discovery, joining by sharing
Ask to join - Visible in discovery, anyone can ask to join from the discovery view
Anyone can join - Visible in discovery, anyone can join automatically
Posting & Commenting permissions:
Set who can create posts and comments in the channel discussion.
Anyone can post and comment (default)
Anyone can comment, but posting is restricted to channel owner and editors
Only the channel owner and editors can comment and post