If you have your notifications on select you will get a bubble icon on your screen. If not, you may have a red dot on your app:
You can pull down your notification and see who has chatted with you:
Select the message and you will be brought straight to Chatter:
You can chat back to them through the Shuffle app:
Curious How will non-Shuffle Users use Chatter?
See this in action on our Shuffle by Elify YouTube Channel: