This is something cool and very straightforward to use. Why did I discover it?
Well, in our intranet we have 200 subsites, and we have workflows everywhere which assigns tasks to people for approval of content.
These tasks are standard Task Lists in Sharepoint. This feature works either with Tasks or Workflow Tasks.
My first though, well, why not create a Content Search WebPart with a query based on content type and Assigned To Me.
After reading a lot I found the My Tasks would do the job pretty well, but it needs some configuration.
My tasks can be found on My Site, My Tasks on the left navigation.
This will show the personal tasks, tasks aggregated by Sharepoint from all Site collections, and if you have also Project Server and Exchange 2013.
In my case, I am not worried about project server or exchange server. I just want to show the workflow tasks.
Instead of copy paste, here are some links to read and know how to setup this feature.