Channels have privacy settings that determine who can view or add to them.

Open channels are (green) channels that anyone can view and add to. You can connect anything you see on to an open channel.

Closed channels (dark purple) can be seen by everyone, but can only be edited by invited collaborators.

Private channels (red) can only be seen or edited by invited collaborators.

You can choose the privacy setting when you create a channel. No matter what privacy setting you use, you can invite other members in the Collaborators tab at the top of the channel page.