Microsoft Teams allows you to add tab in channels. A tab can consist of a document (such as Word) or an app (such as Planner).
To add a tab in a channel, first select the channel you wish the tab to be created in.
Step 1: Click on the '+' icon in the top bar of the channel.
Step 2: In the next window, select the type of document or app you wish to be displayed in the tab.
Step 3: In this example, we will add the Planner app. You are able to create a new plan or use an existing plan from this team. In this example we are creating a new plan called 'Plan01'. Click Save.
Step 4: The tab now consists of our new plan called 'Plan01'.