First of all, to use the task's functionality you must enable this option in Planner.
How to activate Tasks
Access Project Settings
Now, click on Task Fields
How to create a task
To create a task you must follow the following steps:
Double click on the stop where you want to create one or more tasks
In the side menu that appears, click the "Tasks" icon
Click on the "Create Task" box
The task has already been created. Now click on it and fill in the fields such as task name, barcode and comments.
In addition, you also have the option of uploading the tasks from an Excel file.
Learn in detail about the usability of tasks here.