A discontinued feature in Blink, Channels no longer exist for new users from June 2018.
A Channel was a special type of chat accessible only by the members of a Team. When new people were added to the Team, they automatically joined all of it's Channels.
Channels had their good points, particularly with onboarding, but were not widely used and were ultimately confusing to most users.
Blink now only has simple chats. To see or to access the content of a chat, you need to be a member. Chat membership has nothing to do with the Team(s) you might be a member of.