The following is taken from the official Microsoft Blog
Recently Microsoft announced Tasks in Microsoft Teams, a cohesive task management experience that brings your tasks from Microsoft To Do and Planner into Teams. We’re extremely excited about Tasks, but understand that longtime Planner users might have questions—questions like, “Is Planner going away?”
The short answer is, no, and we’re as committed as ever to Planner. The long answer, and more details about the Tasks in Teams experience, is below.
Tasks in Teams—we’ll refer to it as just “Tasks” for the rest of this post—consolidates personal tasks from To Do and team tasks from Planner into a single, comprehensive view in Teams. In short, To Do and Planner are the task services powering this new experience.
There are two places in Teams where you can access Tasks: as an app in the left siderail and as a tab within individual teams. The app comprises all tasks from To Do and Planner, like the screenshot below. As for the tab, you can think of that as Planner renamed: it functions the same way And just like the current Planner tab, you can add multiple Tasks tabs to a single team. Just keep in mind that the tab is for team tasks; personal tasks from To Do cannot be added to a tab.