You need to do following steps:
Setup your Email server: Appliances -> Connectors -> Email Active Response
Add email to the user: Users -> Edit User -> Add email
Now you can use template or create own rule in Build -> Rules
Mentioned steps are visible in this short video: http://www.solarwinds.com/resources/videos/log-management-how-to-create-rules-in-solarwinds-log-and-event-manager.html
I suggest you to use rules from templates. For example Agent Offline Timeout which notifies you if Agent is offline longer than given time period.