Calendar Overlay in SharePoint 2013

• Using Calendar overlay, we can see other calendar events or project tasks overlaid onto the first calendar view with a different color.
•  Using this option we can see sub site’s calendar or Task List events on the main Calendar and the main Calendar or Task List events on the sub site’s calendar with a different color.
• Using this option we can also see external site’s calendar events and Exchange web services of calendar events.

Refer below Screen Shots