There are several types of events generated in Zabbix:
trigger events - whenever a trigger changes its status (OK→PROBLEM→OK)
discovery events - when hosts or services are detected
autoregistration events - when active agents are auto-registered by server
internal events - when an item/low-level discovery rule becomes unsupported or a trigger goes into an unknown state
Internal events are supported starting with Zabbix 2.2 version.
Events are time-stamped and can be the basis of actions such as sending notification e-mail etc.
To view details of events in the frontend, go to Monitoring → Problems. There you can click on the event date and time to view details of an event.
More information is available on: