The difference between @channel and @here and @everyone in slack

@everyone can only be used in the #general channel, which is a channel that all members (except guests) are automatically added to. This mention will notify everyone in the #general channel whether their availability is set to active or away.

The @here command lets you grab the attention of team members in a channel who are currently active. The @channel command, on the other hand, will send a message to all team members of the channel, whether they are currently signed in and active or not.

@everyone notifies every person in the #general channel, @channel notifies all members of a channel, and @here notifies only the active members of a channel.