If you'd like to set a task within your Loop (i.e. read a certain book, talk to a certain person, etc), head to your intended Loop and click the + symbol in the bottom, then select 'Create a Task'.
Here you can define the details of the task, and choose who will perform the task. You can also optionally set a due date.
Once a task has been set, the receiver can mark the task as complete once they have completed it.