I'm sure you would have got a good idea of Permissions by now. Just one more final action to be detailed. Yes, you got it right! It's the 'Send messages' action. Sending messages is an integral part of any channel, but how will including this action under Permissions be used effectively?
Consider this scenario: The HR in your company wants to keep everyone updated on new policies, events, recruitment drives, etc... So now the HR is looking for a way to put forth all this to everyone as announcements. This can be done easily through Permissions. All that the HR should do is, create an Org Channel #HR announcements and then disable 'Send Messages' action under Permissions. The 'Mention users' action will also be disabled by default. Now, only the HR can send messages preventing other users from spamming the channel.
To know more about Channels and its features, check out the Help doc
here. If still you have queries, then feel free to comment.
Now it's time to go ahead, create channels, add members, assign roles and check out permissions!!!