Event Viewer is a built-in Windows tool that displays detailed information about significant events (for example, programs that don’t start as expected or updates that are downloaded automatically) on your computer.
Event logs are special files that record significant events on your computer, such as when a user logs on to the computer or when a program encounters an error. Whenever these types of events occur, Windows records the event in an event log that you can read by using Event Viewer. Advanced users might find the details in event logs helpful when troubleshooting problems with Windows and other programs.
One simple example of how Event Viewer can be used is in pin-pointing the date a problem started so that you can have an accurate date and time to work with when using System Restore.