Sometimes, you might learn about a channel without having been directly invited/subscribed to it (for instance, because someone sent you a channel link).
To subscribe, just follow these steps:
1. Open the channel you want to subscribe to (in most cases, by clicking a link).
2. At the top, click Subscribe.
That's it – you're now subscribed!
The channel will now appear in your left sidebar under CHANNELS. The subscriber icon by the channel name indicates you're a subscriber:
Note: When you subscribe to a channel, you become a subscriber on all that channel's boards.