To indicate areas of your model that need to be analyzed, you can add 2D markup 
and 3D pins 
to the viewing area. When you save your markup, a snapshot is automatically created that contains your markup. To save a pin, click Capture Snapshot 
(pins can also be saved to a snapshot if you add your pins followed by a markup). Snapshots are private in your model file. However, you can easily share this information with others by adding the snapshot containing your markup or pin to a story. When you share the story, all collaborators can see the snapshots you added, review them, and respond to comments associated with the markup and pins.
For more information about stories, see Introduction to stories.