Document reviews are unique to each document.

They can be set to : Annually, every 2 years, every 3 years.

Owners will be reminded via email one month prior to their review date. The email looks like this :

When you click on your dashboard, the task will NOT appear there. Instead, go to the document that is up for review and you will see a Mark As Reviewed Button. 

Make sure everything is up to date and click it.

Your document is now reviewed.