Working in Teams channels
Teams are made up of channels, which you can create under each team in Microsoft Teams. You can create channels for various functions or groups of people. Working in sub-channels is just like operating in the main channel (General).
Channels can be standard, which are for all team members or private channels when only the persons added to the channel can access them.
Private channels are visible only for its members but not others. A lock sign is shown after the private channel’s name to those who are members of the private channel.
Channels allow you to have conversations, online meetings and share files. The new channel has two tabs as default, Posts and Files.
If you want, you can add new tabs, e.g., various applications (Planner, Forms, etc.) or you can pin a specific file from the file library as a tab. You can add applications with the + button.
Creating a channel in Teams (Microsoft support)
Learn about teams and channels (Microsoft support)