The Alerts icon is located in the upper right of ACP. The Alerts icon is represented by the triangle with an exclamation point and a number to the right of the triangle. 
The number represents the number of notification you currently have in ACP. 
When you click the alerts icon, a list of alerts will be displayed.  The alerts are automated alerts from ACP and are based upon your preferences.  
The alerts are to make you aware of issues that need your attention and feature a priority.  Each alert has a color block next to it.  This color indicates the degree of urgency.  Green is mild and informational and does not generally require immediate action. Yellow is more urgent and my require attention. Red is urgent and requires immediate attention. 
The alerts you receive are based on your alert and notification setting.  To review this setting, click the Accounts setting icon and then click settings. You will then be directed to the Alert Default Subscriptions page.  This is where you can change your Alert Settings.