Note: The following text is directly lifted from the Official Warpcast Blog, you can find the original page here.

What are channels?

• Channels are feeds of casts organized around a topic
• Channels are global feeds*

How can I cast in a channel?

• Tap on the channel feed and then tap the new cast button. There should be a label on your draft cast indicating it will be a cast in a channel.
• Reply to a cast already in a channel
• Start composing a new cast and tap the channel selector dropdown menu

Who can cast in a channel?

• Everyone is able to cast in a channel

When I cast in a channel, who sees the casts?

• All casts in channels are public; anyone viewing the channel will see your cast
• Casts in a channel will automatically appear in your followers Home feeds if:
  • They follow the channel and follow you
  • Recasting a cast in a channel will appear in your followers Home feed like a normal recast—even if they don’t follow the channel

Example 1