How to Use Annotations in Google Analytics

Annotations are feature introduced into Google Analytics in early 2010. They allow a webmaster to mark up specific dates on their Analytics page to mark when certain events took place. For example, if you do a site redesign and want to see how traffic patterns look before and after that change you can use the annotations feature to help you remember the date you completed your site redesign. 

Steps

1. 

   Press tab under chart
2. 

   Press create new annotation
   Press create new annotation in the lower right corner.
3. Enter the date and write the description of the item. Select your visibility preference. Press save. Your annotation and your user name will now be visible next time this page is viewed.
   

   Describe event and save

   Source : wikihow.com