How to be notified you about team mates tasks

The person who created the task will always be notified about ant updates, comments or completion.
Also task’s Assignee or Participants will be notified.

When you create task for someone, simply assign it to them and both you and them will be notified.
If a person creates a task and you want to be notified about progress, ask them to add you as Participant. Or you can modify the task and add yourself as Participant.