When you follow a task it means that every time someone changes its name or description, changes the deadline, comments on it, uploads or attaches a file to it - you’ll be notified about it. And the most important thing - if someone checks the task as “DONE” - you’ll be notified.
You follow the task automatically if: you were the one who created it, it was assigned to you, you commented on it, or uploaded or attached a file to it. If you did none of those things, you could just click “FOLLOW”. Or do something about your antisocial tendencies.
To unfollow the task, mouse over the “following” button and click on the “don’t follow” button. The notifications will stop. Nice teamwork, you!