When a Sagan is shared directly to you by someone, it is added to the "Shared with me" tab in your Sagan palette. Here's how to find it:
Go to Map View (the top-down view of your Sagans)
Click the button shown to open the Sagan palette.
Click on the "Shared With Me" tab to see all the Sagans people have shared with you.
Click and drag to add a Sagan to your map.
Shared Sagans are highlighted in green once they are dragged onto your map.