There are two main trigger types, Time trigger (which was used in VC2) and Event trigger. When an event is fired, the associated job will run.
One job can include several triggers, time and/or event based at the same time. A trigger can expire in different ways. A time trigger can expire at a certain date. An event trigger can expire at a certain date or after a certain number of trigger events.
The individual trigger types are available when the Add job, Edit job or Clone job dialog is open. By clicking on the Triggers tab and the Add button you can see the list of triggers (empty when adding a new job).
Clicking Ok will save the trigger to your job. Remember that when editing or adding a job, the trigger is not saved and active until you click Ok on the Add job window.