Whenever somebody interacts with you or your content on community, or when you receive a new badge or rank, you can choose to receive notifications. You can easily configure how you'd like to receive notifications; some people prefer to just have notifications show when they are logged into community, whilst others like to receive email or pop up notifications on their smartphone when somebody replies to their posts so that they don't forget.
You can customise and change these settings at any time. To do this, simply click on 'Notification Settings' in your Account Settings hub. You can then customise how you'd like to receive notifications for different alerts.