A circle the basic unit of Mentza and is a 20 minutes live audio conversation which allows for 5 speakers and any number of listeners. You can create a circle, join a circle as a speaker or just listen to a conversation. You can switch from being a listener to a speaker (in case a speaker slot is free) by tapping on the "Join Speakers" button on the live call screen. Also, you can switch from being a speaker to a listener by tapping on your profile pic and choosing the swap to listener option
Channels are circles that recur at a fixed frequency - Daily, Weekly, Bi-weekly or a number of times a week. Channels allow people to follow the channel and hence get notified closer to the time the next episode goes live.