Click Browse channels in the sidebar to open the directory. Lists every public channel in your realm plus any area channels.
What each row shows
Channel name.
Description (when set).
Member count.
Joining
Public channels — click Join. You're in immediately.
Area channels — Join is replaced by "Via area access" because membership flows from area access rather than channel join.
Note — Private channels don't appear in the directory — they're only visible to members and to people invited by an owner.
Searching
The search box at the top of the directory filters by channel name in real time.