Push notifications are the key to how you know that you've gotten a new message, new like or any new content or promotions that are posted inside the app.  You can turn push notifications on and off inside of the app by going to My Profile > Settings > Push Notification Settings and then tap the toggle to the setting you'd like.  

If you have any issues receiving push notifications, be sure to check your phone's general settings to see that you have notifications turned on for HER.