Now your Rule has been created then you can specify what Actions are to take place when the Rule is triggered.  In the Action tab press [New] to launch the Action pop up.

Select Type - this will display all the current actions available, select 'Add Notification' and the field to the right will update its label based on the Type you have selected.

Fig 1 - Notification selection

The Recipient field drop down will display all the Users in your account, you can select as many People as you wish to be notified.  You can use the magnifying glass icon next to the drop down list to open up the Find screen, this will show all the Users with additional details such as email address.

Notifications are sent to the Notification area on the top right of the screen.

Fig 2 - Notification information