First you have to join the FileMaker Community (see blue nav bar at the top of the screen).
Then you have to Sign In (again, the blue nav bar).
Then, when you visit the group, you'll see a "Follow" button in the upper right of the "FileMaker Developer Challenge 2016" banner.
Click it, and you'll be following the group.
You can set email preferences as part of your Preferences (this link appears in the drop-down associated with your avatar on the blue nav bar).