Channels are how messages are sent and received. Clients that subscribe to a channel will receive messages that are published on that channel.
Channels are very lightweight and flexible. Channels exist merely by using them. Just publish or subscribe to a channel name and nothing more.
And, use as many channels as your app requires. There is no additional charge for the number of channels you use. But, you should use them in a way that makes the most sense for your use case.
And a channel is just a channel. What you use it for is completely up to your application’s requirements. For example, a channel might be used for 1 to 1 private chat, many to many group chat, 1 to many broadcasting, or many to 1 fan-in. And a channel that is being used for private chat can suddenly be used for group chat. It is just up to you to allow more users to start subscribing and publishing to that channel.
So channels are just blank communication devices for which you determine the actual usage.