You can change who can post messages in the #general channel. This channel will be read-only for anyone without permission to post.

1. From your desktop, open the #general channel.
2. Click the channel name in the conversation header.
   
3. Select the Settings tab.
4. Next to Posting permissions, click Edit. 
5. Select who can post and reply to messages. If you're specifying specific people, you can select up to 100.
6. Click on Save changes.

You can change who can post in any channel. A channel will be read-only for anyone without permission to post.

1. From your desktop, open the channel that you’d like to adjust posting permissions for.
2. Click on the channel name in the conversation header.
3. Select the Settings tab.
4. Next to Posting permissions, click Edit. 
5. Select who can post and reply to messages. If you're specifying specific people, you can select up to 100 per channel.
6. Click on Save changes.

You can change who can use @everyone to notify all members of the #general channel. 

1. From your desktop, open the #general channel.
2. Click on the channel name in the conversation header.
3. Select the Settings tab.
4. Next to Posting permissions, click Edit. 
5. Tick or untick the box next to Allow @everyone mentions.
6. Click Save changes.

You can change who can use @everyone to notify all members of the #general channel. You can also change who can use @here or @channel to notify members in other channels.

1. From your desktop, open the channel that you’d like to adjust posting permissions for.
2. Click on the channel name in the conversation header.
3. Select the Settings tab.
4. Next to Posting permissions, click Edit. 
5. Tick or untick the box next to Allow @here and @channel mentions. (For the #general channel, you’ll see Allow @everyone mentions.)
6. Click Save changes.