To follow the progress of a task, you can subscribe to it. You can subscribe others as well. This allows any subscribedusers to be notified when tasks get changes or status updates.

Whoever creates, comments, assigns, or is tagged in a comment of a task will automatically become a subscriber.

You can find and add subscribers to any open task at the bottom right of the task box. To add someone new, simply hover over "subscribers" and click. A new menu will open that will list all team members associated with the dartboard. Choose whomever you would like to add to subscribe them to the task:

To unsubscribe from a task, go to the "more" button at the top right of your task screen and choose "unsubscribe" from the menu.

You can also find the checkbox for subscribers in the notification settings.

Go to: Settings > Notifications and then choose to be notified of subscriber changes on tasks you have created/are subscribed to. You can choose to be notified either in-app, by email, or both.