I am new to using ciscoworks and I would like to have ciscoworks notify me by email is a device gets disconnected from the network.
Device Fault Manager will give you what you want. You should read the online help under the DFM > Notification Services component to get all of the details on setting this up. Basically, you will create a new Notification Group for the devices in which you are interested. Here, you should only check the boxes for Events (not Alerts). You can further refine which Events are sent as notifications by configuring Event Sets (again documented in the online help).
Once you have the Notification Group to your liking, you will create a new Email Notification Subscription. This will tie the Notification Group you created to one or more email addresses.
Then you're done. Anytime DFM generates an Event that matches your Notification Group, you will get an email with the details.