Tasks are items of work that need to be performed before a job can be completed. If any tasks are assigned to a job, they can be viewed underneath "Notes" in the "Tasks" section.
To see if any tasks have been applied to a job, open the job in question and scroll down until you can see the notes section. Tasks appear below "Notes," in the "Tasks" section.
To complete a task, a resource must tap on the related field in the job details. A blue tick will appear on the right side of the task to show that it's been completed. It is possible to toggle a task on and off, but all tasks must be checked (ticked) before a job can be completed.
By default, tasks are mandatory. There is an admin setting ("Consider job tasks to be optional") that can be enabled to allow resources to complete jobs even when not all the tasks have been completed.