Microsoft To Do connects with Planner, so that you can have all your work tasks from that service displayed in one application.
To have this functionality activated, you must go into the settings in Microsoft To Do, and enable Planner as a connected application.
Note! Not all tasks in a KANBAN board in Planner are displayed in To Do. Only the tasks in the KANBAN board assigned to you will appear in To Do.
Tasks given to you from shared lists in To Do and from the KANBAN board in Planner will appear together under the automatically generated list Assigned to me.